Ryan Meier Dissertation final copy - Vanderbilt Universityetd.library.vanderbilt.edu/available/etd-07032012-151321/unrestricte… · without whom, none of the work presented in this

MANGANESE(II) INDENYL COMPOUNDS: SYNTHESIS, CHARACTERIZATION AND

REACTIVITIES WITH OXYGEN DONOR LIGANDS

By

Ryan M. Meier

Dissertation

Submitted to the Faculty of the

Graduate School at Vanderbilt University

in partial fulfillment of the requirements

the degree of

Doctor of Philosophy

in

Chemistry

August, 2012

Nashville, Tennessee

Approved:

Timothy P. Hanusa

C.M. Lukeheart

David Wright

James Wittig

ii

Copyright © 2012 Ryan Matthew Meier All Rights Reserved

iii

To my friends and family, especially my parents, for all of their patience, support, and

sacrifices over my decades of schooling.

iv

ACKNOWLEDGEMENTS

This work would not have been possible without the help and contributions of a

large number of people and orginizations. First, I would like to thank the groups

responsible for the funding of myself and the projects during my time at Vanderbilt,

without whom, none of the work presented in this dissertation would have been possible.

The Petroleum Research Fund and National Science Foundations both contributed grant

money to pay for chemicals and supplies as well as my stipend for my year as an RA. A

thanks also goes out to the Vanderbilt Chemistry department for their funding me as a

teaching assistant and fellow for my first 4 years of graduate school. A special thanks

goes out to the Graduate School at Vanderbilt for their support through a dissertation

enhancement grant that helped take some of this work to a whole the edge of publication,

and make it possible to hopefully over that edge in the near future.

There are a number of influential people who greatly impacted my education over

the years that I would also like to thank, starting with all of my general chemistry teacher

Professor David Cedeno, who was the first teacher to get me truly interested in chemistry.

Next are all of my undergraduate chemistry professors at Knox: Diana Cermak, Linda

Bush, Thomas Clayton, Lawerence Welch, Andrew Mehl, and Mary Crawford. On top

of being fantastic teachers whom not only gave me an education that prepared me well

for graduate school, they also gave me a great appreciation of the teacher-student

interactions at a liberal college. This appreciation is something that I still hold on to

today and is one of the biggest reasons I will now be a professor at a liberal arts college

myself.

v

I would also be remiss not to thank my committee, Charles Lukehart, David

Wright, Jim Wittig, and Timothy Hanusa, for their valueable insight and guidance over

my years in graduate school. A particularly special goes to my advisor, Dr. Hanusa, for

always being there when I had questions and being the best boss and roll model for a

future professor that I could have possibly imagined. The way he cares about his

students, whether in his research group or simply in his general chemistry class, his

passion and work ethic are an inspiration to me, and I aspire to one day be as good of a

teacher as he is.

The hardest part about graduate school is often just the grind of research when

things aren’t going well. Thankfully the other students in the chemistry department are

always understanding of this and continually come together to help give each other

activities and adventures to help make the grind more bareable for everyone involved. I

will truly miss all the days of intramural sports and nights spent playing trivia that helped

make the whole graduate experience considerably easier to endure.

Last, I need to thank the most important people of all, my family, particularly my

parents, for everything they have done for me over the past 26 years. I would not have

had the amazing opportunities to go to Knox and Vanderbilt if my parents had not

sacrificed so much of their time and money to allow me to pursue my dreams. I can’t

thank them enough, and I can only hope I am able to give the same opportunities to my

children in the future that my parents gave to me.

vi

TABLE OF CONTENTS

Page

COPYRIGHT ...................................................................................................................... ii

DEDICATION ................................................................................................................... iii

ACKNOWLEDGEMENTS ............................................................................................... iv

LIST OF TABLES .......................................................................................................... viii

LIST OF FIGURES .............................................................................................................x

LIST OF ABBREVIATIONS .......................................................................................... xiv

Chapter

I. SYMMETRY AND STERIC EFFECTS ON SPIN STATES IN TRANSITION METAL COMPLEXES .............................................................1

II. STRUCTURAL FEATURES OF ORGANOMANGANESE COMPOUNDS .....33

III. SYNTHESES AND STRUCTURES OF SUBSTITUTED

BIS(INDENYL)MANGANESE(II) COMPLEXES ..............................................65

Introduction ............................................................................................................65

Experimental ..........................................................................................................66

Results ....................................................................................................................75

Discussion ..............................................................................................................84

Conclusion .............................................................................................................86

IV. SYNTHESES, STRUCTURES, AND REACTIVITIES OF

MONO(INDENYL)MANGANESE HALIDES ....................................................88

Introduction ............................................................................................................88

vii

Experimental ..........................................................................................................92

Results ..................................................................................................................101

Discussion ............................................................................................................115

Conclusion ...........................................................................................................120

V. SYNTHESIS AND CHARACTERIZATION OF MANGANESE(II)

COMPLEXES OF BULKY ARYLOXIDES ......................................................121

Introduction ..........................................................................................................121

Experimental ........................................................................................................122

Results and Discussion ........................................................................................128

Conclusion ...........................................................................................................133

VI. PROJECT SUMMARY AND FUTURE RESEARCH .......................................135

Summary ..............................................................................................................135

Future Work .........................................................................................................136

Appendix

A. CRYSTAL DATA AND ATOMIC FRACTIONAL COORDINATES FOR X-RAY STRUCTURAL DETERMINATIONS .................................................139 B. SOLID STATE MAGNETIC DATA ..................................................................160

REFERENCES ................................................................................................................163

viii

LIST OF TABLES

Table Page

1. Distribution of Mn-C and Mn…Mn bonds in Organometallic Compounds ...........37

2. Select bond distances and averages for [K(dioxane)1.5][(Mn(Ind2Me-4,7)3] ............80

3. Selected bond distances of (Ind3Me-2,4,7)2Mn ..........................................................83

4. Selected bond distances for [(Ind3Me-2,4,7)MnCl(thf)]2 .........................................103

5. Selected bond distances for [(IndMe-2)MnI(thf)]2 .................................................105

6. Selected bond distances for (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) ...........................130

7. Selected bond distances for (BHT)2(µ-BHT)Mn2(µ-Cl) .....................................132

8. Crystal Data and Structure Refinement for K(dioxane)1.5][(Mn(Ind2Me-4,7)3] ......140

9. Fractional Coordinates and Isotropic Thermal Parameters for Non-hydrogen

atoms in K(dioxane)1.5][(Mn(Ind2Me-4,7)3] ............................................................141

10. Crystal Data and Structure Refinement for (Ind3Me-2,4,7)2Mn ...............................144


atoms in (Ind3Me-2,4,7)2Mn .....................................................................................145

12. Crystal Data and Structure Refinement for [Ind3Me-2,4,7MnCl(thf)]2 ....................146


atoms in [Ind3Me-2,4,7MnCl(thf)]2 ..........................................................................147

14. Crystal Data and Structure Refinement for [IndMe-2MnI(thf)]2 ............................149


atoms in [IndMe-2MnI(thf)]2 ..................................................................................150

16. Crystal Data and Structure Refinement for (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) ...151

ix


atoms in (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) .........................................................152

18. Crystal Data and Structure Refinement for (BHT)2(µ-BHT)Mn2(µ-Cl) .............154


atoms in (BHT)2(µ-BHT)Mn2(µ-Cl) ....................................................................155

20. SQUID data for [Ind3Me-2,4,7MnCl(thf)]2 ..............................................................161

x

LIST OF FIGURES

Figure Page

1. Structures of [Fe(bipy)3]2+ cation, [Fe(3,3´-Me2-2,2´-bipyridine)3](PF6)2,

[Fe(1,1´-biisoquinoline)3]2+. ....................................................................................4

2. Solid state structures of [Fe(phen)3]2+ and [Fe(2-Me-phen)3]2+ ...............................6

3. Solid state structure of [Fe(2,9-Me2-phen)2(NCS)2]. ...............................................7

4. Structures of 6-Me-bipy and 6,6´-R2-terpy ..............................................................8

5. Structures of 4,4´-dimethyl-bi-2-thiazoline, 2,6-di(1H-pyrazol-3-yl)pyridine,

(2´-pyridyl)imidazoline, (6´-methyl-2´-pyridyl)imidazoline ..................................9

6. Solid state structure of [Fe(HB(3,4,5-(Me)3(pz)3)2] ..............................................10

7. Structures of [1,4,-(2´-pyridyl)2-7-(6´-R-2´-pyridyl)]-triazacyclononane and

bis(2-pyridylmethyl)amine ....................................................................................11

8. Solid state structure of bis(2-methylimidazole)(octaethylporphinato)iron(III) .....12

9. Structure of FeIII cyclamacetate model complex ...................................................13

10. Structure of tpen (R = H) and mtpen (R = Me). Solid state structure of

Fe[mtpen]2+ ............................................................................................................14

11. Structure of tris[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine and solid state

structure of Fe[tris[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine]2+ ........................15

12. Structure if 2-pyridinalpheylimine model compound ............................................16

13. Structures of the substituted pyridine ligands (23), (24), and (25) .......................16

14. Solid state structure of Octaisopropylmanganocene ..............................................19

15. Solid state structure of [Mn{1,3,4-(Me3C)3C5H2}2] ..............................................20

xi

16. SQUID magnetometry data for [Cr(Cp4i)2] showing its SCO behavior ................21

17. Solid state structures of [Fe(L1)(HIm)2]ClO4 and [NaFe(L2)(HIm)2(ClO4)2] ........22

18. Indenyl ligand with numbering scheme .................................................................23

19. Qualitative molecular orbital diagram for bis(indenyl)chromium(II) with a

staggered conformation ..........................................................................................24

20. Qualitative molecular orbital diagram for bis(indenyl)chromium(II) with a

gauche conformation ..............................................................................................24

21. Solid state structures of bis(2-methylindenyl)chromium(II) (staggered) and

bis(1-methylindenyl)chromium(II) (eclipsed) .......................................................27

22. Partial unit cell of bis(2,4,7-trimethylindenyl)chromium(II) showing both

staggered and eclipsed conformers ........................................................................29

23. SQUID magnetometry data for methylated bis(indenyl)chromium compounds ...30

24. SQUID magnetometry data for bis(indenyl)chromium(II) compounds with

t-Bu and SiMe3 substitutions .................................................................................31

25. Solid State structures of [Cr(1,3-(t-Bu)2C9H5)2] and [Cr(1,3-(i-Pr)2C9H5)2] .........32

26. Spread in manganese-carbon single bond lengths; on the left, including M–CO

bonds; on the right, with M–CO and M-cyano bonds omitted ..............................37

27. Structures of selected organomanganese compounds exhibiting noteworthy

Mn-C bond lengths .......................................................................................... 38-39


Mn=C bond lengths ...............................................................................................40

29. Spread in manganese-carbon double bond lengths ................................................40

xii


Mn≡C bond lengths ................................................................................................41

31. Cymantrene as an organometallic substituent and as a 16e– fragment bound

to a metal ................................................................................................................42

32. Solid state structures of notable cymantrene-like compounds (48) and (49) .........43

33. Solid state structures of notable cymantrene-like compounds (50) and (51) .........44

34. Spread in Mn-C(Cp) distances in mono(cyclopentadienyl) manganese

complexes ..............................................................................................................45

35. Solid state structure of the manganocene derivative (52) ......................................46

36. Solid state structures of manganocene derivative (53) and analogous

structures for (54) and (55) ....................................................................................47

37. Solid state structure of the manganocene derivative (57) ......................................48

38. Solid state structures of notable manganocene derivatives (58) and (59) .............49

39. Solid state structure of a dimeric monocyclopentadienyl manganese halide ........50

40. Spread of Mn-C distances in Cp2Mn complexes ...................................................51

41. Solid state structure of manganocene polymer ......................................................52

42. Gas-phase structure of dimethylmanganocene ......................................................53

43. Solid state structure of decamethylmanganocene ..................................................54

44. Solid state structure of THF solvated manganocene ..............................................55

45. Structures of phosphine adducts of manganocene .................................................56

46. Structures of phosphine and carbene adducts of manganocenes ...........................57

47. Schematics for the CT salts between decamthylmanganocene and various

electron acceptors (71) and (72) ............................................................................58

xiii

48. Structures of triscyclopentadienyl manganate anions (81) and (82) ......................59

49. Rearrangements of the “indenyl effect” .................................................................60

50. Numbering scheme for the indene ligand (75); Solid State structure of THF

solvated bis(indenyl)manganese (84) ....................................................................62

51. Solid state structures for bis(2-trymethylsilylindenyl)manganese (85) and

bis(1,3-diisopropylindenyl)manganese ..................................................................63

52. Solid state structure of bis(1,3-bistrimethylsilylindenyl)manganese .....................64

53. Plot of the non-hydrogen atoms of {(Ind2Me-4,7)2Mn}8 ................................................................78

54. ORTEP of [K(dioxane)1.5][(Mn(Ind2Me-4,7)3] .........................................................81

55. Projections down the crystallographic c (left) and a (right) axes of

[K(dioxane)1.5][(Mn(Ind2Me-4,7)3] ...........................................................................81

56. Polymeric structure of (Ind3Me-2,4,7)2Mn .................................................................83

57. Asymmetric unit of (Ind3Me-2,4,7)2Mn .....................................................................84

58. Solid State Structure of [(Ind3Me-2,4,7)MnCl(thf)]2 ................................................103

59. Solid State Structure of [(IndMe-2)MnI(thf)]2 .......................................................106

60. IR spectra comparison of [(IndMe-2)MnCl(thf)]2 and its oxo-species ...................107

61. UV-vis spectra of [(Ind3Me-2,4,7)MnCl(thf)]2 as oxo-species forms ......................109

62. Resonance Raman spectra for [(Ind3Me-2,4,7)MnCl(thf)]2 and its oxo-species ......110

63. EPR spectrum of [Ind3Me-2,4,7MnCl(thf)]2 ............................................................112

64. EPR spectrum of the oxo-species of [Ind3Me-2,4,7MnCl(thf)]2 ..............................114

65. Zoomed in fragments of EPR spectrum of [Ind3Me-2,4,7MnCl(thf)]2 .....................115

66. Solid state structure of (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) ...................................131

67. Solid state structure of (BHT)2(µ-BHT)Mn2(µ-Cl) .............................................132

xiv

LIST OF ABBREVIATIONS

BHT butylated hydroxytoluene

bipy bypyridine

Cp cyclopentadienyl

Cp* pentamethylcyclopentadienyl

HOMO highest occupied molecular orbital

i-Pr isopropyl

Im imidizole

Ind indenyl

IndMe-1 1-methylindenyl

IndMe-2 2-methylindenyl

Ind2Me-4,7 4,7-dimethylindenyl

Ind3Me-1,2,3 1,2,3-trimethylindenyl

Ind3Me-2,4,7 2,4,7-trimethylindenyl

Ind7Me or Ind* 1,2,3,4,5,6,7-heptamethylindenyl

IndSi-1 1-trimethylsilylindenyl

IndSi-2 2-trimethylsilylindenyl

Ind2Si-1,3 1,3-bis(trimethylsilyl)indenyl

Ind2i-1,3 1,3-diisopropylindenyl

KODipp potassium diisopropylphenoxide

LIESST light-induced excited spin state trapping

LUMO lowest unoccupied molecular orbital

Me methyl

MLCT metal to ligand charge transfer

xv

NIESST nuclear decay induced excited spin state trapping

PVA polyvinyl alcohol

por porphyrin

pz pyrazolyl

SCO spin crossover

t-Bu tertiary-butyl

TCNE tetracyanoethylene

TCNQ tetracyanonapthoquinone

terpy terpyridine

Tp tris(pyrazolyl)borates

Tpp tetraphenylporphinato

CHAPTER I

SYMMETRY AND STERIC EFFECTS ON SPIN STATES IN TRANSITION METAL COMPLEXES

Introduction

Control over the magnetic characteristics of transition metal complexes is a major

research area in inorganic and organometallic chemistry, and is important to the fields of

information storage, imaging science, and molecular switching.1 Such control is typically

achieved by varying the electron donor/acceptor properties of coordinated ligands, but

alterations of temperature, light, magnetic fields, and lattice characteristics (for solids)

can influence the spin state behavior of compounds as well.2 These changes modify the

energies of metal d-electron levels, which affect the overlap of metal-ligand orbitals, and

ultimately alter metal-ligand (M-L) distances. Conversely, manipulation of metal-ligand

distances through pressure or steric effects can affect the strength of the ligand field.

Divalent iron complexes of 1,10-phenanthroline were among the first systems

known in which interligand steric crowding and the associated bond length changes

affected the relative stability of the metals’ spin states. These discoveries of the 1960’s

have been extended to a variety of complexes containing other N-donor ligands such as

substituted pyridines and poly(pyrazoyl)borates, and in more recent years to

metallocenes; they will be described in additional detail below.

Another method of influencing spin states depends on changes in the rotational

conformation of ligands, which through orbital symmetry interactions alter the HOMO-

LUMO gap in a complex. Among the most extensively studied examples of these

2

systems are substituted bis(indenyl)metal complexes, [MInd2], which are related to the

[MCp2] metallocenes. In the latter, the exact rotational conformation of the

cyclopentadienyl (Cp) ligands does not appreciably affect their interactions with d

orbitals. In contrast, the nodal properties of the indenyl ligand are sufficiently different

from those of cyclopentadienyl that in susceptible compounds of CrII, the relative

orientation of the ligands around the metal influences its spin state, giving rise to low-

spin, high-spin, and spin-crossover species. Such “magnetism with a twist” provides an

additional means for designing and manipulating the magnetic behavior of related

substituted species.

A comprehensive review of the magnetochemistry of spin-crossover species is

available;2 but the initial motivation for much of the work in this dissertation was with

regards to the steric and symmetry effects on magnetic spin states. The remainder of this

chapter serves as a literature survey focusing on the manipulation of the magnetic spin

states of molecules through symmetry and steric effects.

Steric Effects on Magnetism in Inorganic Complexes

In many classes of transition metal compounds, metal–ligand distances are

relatively insensitive to steric effects, even though ligand field strengths and the

associated splitting of metal d-electron levels are in fact sensitive functions of M–L

separation. A ligand field analysis of metal complexes with neutral ligands concluded

that ∆o varies as µ/a6, where µ is the dipole moment of the ligand and a = M–L distance.3

Given this order of dependence, ∆o would be reduced by half from a change in metal-

ligand bond length from 2.00 Å to 2.25 Å. Such a bond length change, although

3

substantial, is not unusual for metal ions in different spin states, and there are several

classes of compounds in which steric effects explicitly affect metal-ligand distances

enough to alter the metal’s spin multiplicity. Often these involve spin-crossover (SCO)

species (sometimes called spin transition, spin equilibrium, or spin isomer systems),2 and

the low-spin to high-spin transition in such complexes is entropically favored. The

entropy change (∆S) for the process varies as the log of the ratio of the spin multiplicities

(ln[(2S+1)HS/(2S+1)LS]);3 consequently, among first-row transition metal complexes,

those containing FeII (∆S = ln(5⁄1)) and MnII (∆S = ln(6⁄2)) are the most likely to display

SCO behavior.

In most of the cases described in this chapter, a ligand substituent with somewhat

greater steric demand than a hydrogen atom (often a methyl group suffices) provides

enough steric congestion that metal-ligand bonding is distorted and lengthened, leading to

weaker ligand field strength and higher spin species. Typically the bulkier substituent is

relatively close to the metal center so that the interference in the M–L bonding is directly

apparent, and several categories of these systems will be described in the following

sections.

There are, however, cases where a substituent is remote from a metal and yet the

resulting complex displays high-spin or SCO behavior, even though the compound with

unsubstituted ligands does not. An example of this involves iron complexes of 2,2´-

bipyridine; the unsubstituted [Fe(bipy)3]2+ cation (Figure 1; 1) is low spin at all

temperatures, but the [Fe(3,3´-Me2-2,2´-bipyridine)3](PF6)2 complex (Figure 1; 2)

transitions from low spin at 90 K (µeff = 1.1 µB) to an intermediate spin at 363 K (µeff =

4.0 µB).4 The methyl groups in the 3,3´-Me2-2,2´-bipyridine ligand are not near the metal,

4

and would be expected to increase the donor strength of the ligand through inductive

effects. However, the methyl groups sterically interact with each other, causing a twist

distortion of the ligand, and causing interference with both σ- and π-donation. As a

consequence, the methylated bipyridine is an intrinsically weaker donor than the

unsubstituted ligand. A similar steric influence is found in complexes of the 1,1´-

biisoquinoline ligand (Figure 1; 3).

(1) (2) (3) Figure 1. (1) [Fe(bipy)3]2+ cation. (2) [Fe(3,3´-Me2-2,2´-bipyridine)3](PF6)2. (3) [Fe(1,1´-biisoquinoline)3]2+.

Another issue that arises in this context is the electronic donor effect of a ligand

substituent, as distinct from the effect of its steric bulk. For example, alkyl groups are

frequently considered as net electron donors, regardless of the ligand type to which they

are attached. Such behavior should not be expected in all molecular contexts, however.

Alkyls are donors through induction to conjugated π systems such as aromatic rings, for

example. However, when methyl groups are attached to an amine, they can function as

electron-withdrawing groups, owing to hyperconjugative effects.5 Thus the presence of

an alkyl group on a non-conjugated ligand can weaken the ligand field strength through

both steric and electronic effects, and it may not always be possible to determine which,

if either, has the stronger influence.

5

Diimines and Terimines.

The first example of a synthetic FeII SCO species was reported in the 1960’s,

when the thermally induced 5T2g 1A1g spin transition in [Fe(1,10-

phenanthroline)2(NCS)2] was described.6 This discovery prompted much interest in the

SCO behavior of divalent iron complexes, in part from to the ability to analyze such

species with Mössbauer spectroscopy. Divalent iron complexes of 1,10-phenanthroline

were also among the first systems known in which interligand steric crowding and the

associated bond length changes were identified as affecting the relative stability of the

metal spin states.

For example, the complex [Fe(phen)3]2+ (phen = 1,10-phenanthroline) (Figure 2;

4) is diamagnetic at all temperatures, but the related methyl-substituted complex [Fe(2-

Me-phen)3]2+ (Figure 2; 5) is a SCO species, and strongly paramagnetic at room

temperature (S = 2). These results would be counterintuitive if the stronger σ-donor

ability of the methyl group relative to hydrogen in aromatic rings was considered by

itself. The methyl groups of [Fe(2-Me-phen)3]2+ plainly interfere with the metal–ligand

bonding, however. This is evident in the asymmetry in the Fe–NMe and Fe–NH distances

in the crystal structure of the compound (2.25 Å and 2.17 Å, respectively, at 298 K), a

difference that would be exacerbated in a low-spin FeII environment. The resulting

weaker ligand field strength is also reflected in the longer avg. Fe–N distances in 5 (2.21

Å) compared to those in 4 (1.98 Å), typical for high-spin and low-spin Fe–N distances,

respectively. The congestion around the metal center is such that attempts to form the

[Fe(2,9-Me2-phen)3]2+ ion have been unsuccessful.7

6

(4) (5) Figure 2. (4) [Fe(phen)3]2+. (5) [Fe(2-Me-phen)3]2+.

In nuclear decay induced excited spin state trapping (NIESST) experiments, FeII

complexes can be generated from the radioactive decay of precursor 57CoII complexes,

and their Mössbauer spectra collected. Such experiments have demonstrated that [57Fe(2-

Me-phen)3]2+ is initially generated in a long-lived high-spin (5T2) excited state even at 4.2

K, a temperature at which the ground state would be low-spin.8 Light alone can induce a

high-spin state in 5 embedded in a PVA film; LIESST (light-induced excited spin state

trapping) experiments have demonstrated that irradiation of 5 with 514.5 nm light at 12 K

will bleach the MLCT band characteristic of the low-spin state. If the temperature is held

below 40 K, the high-spin excited state can persist for hours.9

Balancing the donor/acceptor properties and steric bulk of a ligand can also be

used to tune the ligand field strength. Owing to the stronger donor properties of a

methoxy group compared to methyl, the 2-CH3O-substituted analogue [Fe(2-(CH3O)-

phen)3]2+ requires higher temperatures for the SCO to occur than in 5. Conversely, the 2-

Cl-substituted variant is persistently high-spin, aided by the electron-withdrawing

properties of the chloride ligand.

7

The same effects of methylation on spin states is observed in other 1,10-

phenanthroline derivatives such as [Fe(2-Me-phen)2X2] (X = Cl, Br, NCS, N3), and

[Fe(2,9-Me2-phen)2(NCS)2]. These are high-spin species between 78 K and room

temperature; the corresponding unsubstituted (or 4-Me-, 5-Me-substituted) analogues are

low spin or exhibit SCO behavior. The X-ray crystal structure of [Fe(2,9-Me2-

phen)2(NCS)2] (Figure 3; 6) reveals the distortions induced by the methyl groups; in

particular, the Fe–NCS bond distances are extremely long (2.316(3) Å avg.) owing to

multiple close contacts (< 4 Å) with the phenanthroline ligand (the avg. of all four Fe–

Nphen distances is 2.27(5) Å). The iron atoms lie an avg. of 1.04 Å out of the place of

the phenanthroline ligands in 6, compared to a displacement of only 0.077 Å for

[Fe(phen)2(NCS)2]. These distortions serve to weaken the π-back donation to the iron,

and help support the high-spin state in the complex.10

(6) Figure 3. [Fe(2,9-Me2-phen)2(NCS)2].

As noted at the beginning of Section 2, derivatives of 2,2´-bipyridine also display

sterically induced SCO. The use of methyl substitution at the 6-position in bipyridine

(Figure 4; 7) leads to an SCO FeII species, whereas the unsubstituted [Fe(bipy)3]2+ cation

is low spin. As is the case with 1,10-phenanthroline, steric congestion prevents formation

of the [Fe(6,6´-Me2-bipy)3]2+ derivative. Terpyridines are similar to the bipyridines in

8

that the unsubstituted iron complexes are low spin, but when R1 is phenyl, the resulting

complex displays SCO behavior. Terpyridines containing methyl or phenyl groups at

both the R1 and R3 positions (Figure 4; 8) are isolable, and are high spin in both the solid

state and in solution.11

(7) (8) Figure 4. (7) 6-Me-bipy. (8) 6,6´-R2-terpy.

It should be noted that, all else being equal, SCO behavior is more difficult to

induce in complexes containing five-membered heterocyclic ligands than in their six-

membered counterparts. Geometric considerations place substituents farther away from

the metal center in the former, where they are less able to cause steric crowding. Thus

not only can a tris FeII complex of 4,4´-dimethyl-bi-2-thiazoline (Figure 5; 9) be

generated (which as noted above, is not possible for 2,9-Me2-phen), but the complex is

low spin even at room temperature.12 However, when both 5- and 6-membered rings are

involved, as in some analogues of terpyridine (Figure 5; 10) or imidazoline (Figure 5;

11), SCO transitions can be observed in the resulting iron complexes. If the bulk of 11 is

augmented with a methyl group to produce the (6´-methyl-2´-pyridyl)imidazoline ligand

(Figure 5; 12), its yellow FeII complex displays a magnetic moment between 77–298 K

that is consistent with a high-spin ground state; its magnetic susceptibility follows Curie-

Weiss behavior.13

9

(9) (10) (11) (12)

Figure 5. (9) 4,4´-dimethyl-bi-2-thiazoline. (10) 2,6-di(1H-pyrazol-3-yl)pyridine. (11) (2´-pyridyl)imidazoline (12) (6´-methyl-2´-pyridyl)imidazoline.

Pyrazolylborates

Tris(pyrazolyl)borates and the related pyrazolylmethane derivatives are well-

studied systems that can display SCO behavior. [Fe(Tp)2] (Tp = HB(pz)3) is weakly

paramagnetic from 78 K to room temperature, but transitions at ca. 380 K to the 5T2g

ground state, assisted by a crystallographic phase change. The 3,5 derivative is high spin

at room temperature but converts to the low-spin state at 150 K, and the 3,4,5 analogue is

essentially high-spin at all temperatures between 40 and 295 K. The methyl group in the

4-position was originally thought to interfere with the normal contraction of the lattice on

cooling, hence blocking the spin state change.14 Recent investigations on the trimethyl

substituted compound (Figure 6; 13) and related complexes containing cyclopropyl

substituents have shown that intramolecular interactions lead to twisting of the pyrazolyl

rings, and interfere with the bite angle of the ligands. If the FeN–NB torsion angle is

greater than about 11°, complexes that are high spin at room temperature will not display

SCO behavior on cooling.15

10

(13)

Figure 6. (13) [Fe(HB(3,4,5-(Me)3(pz)3)2].

Much of the complex magnetic behavior of poly(pyrazolyl)borate complexes is

observed only in the solid state; in solution, both [Fe(HB(3,5-(Me)2(pz)3)2] and 13 are

high-spin between 200 and 295 K, and even the unsubstituted [FeTp2] displays a

magnetic moment of 2.71 µB in CH2Cl2 at room temperature, consistent with a mixture of

high- and low-spin species.

An indirect steric effect that supports the low-spin state occurs when the hydrogen

on the central boron is substituted with an additional pyrazolyl ring or a phenyl group;

e.g., [Fe(B(pz)4)2] and [Fe(PhB(pz)3)2] are low spin in solution. Intraligand steric

crowding is thought to compress the other ligands, generating a smaller bite angle that

favors low-spin FeII.16

Macrocyclic systems

The strong field ligand 1,4,7-triazacyclononane is the basis for a hexadentate

ligand system that supports the low-spin state of FeII.17 When a single methyl group is

added to the 6-position in one ring (Figure 7; 14; R = Me), the steric influence causes the

11

complex to display SCO behavior. It has been argued that the activation process for the

spin state change in solution involves a trigonal twist motion, and the relatively high

value of the activation parameter for the quintet-singlet transition in the FeII complex of

14 with R = Me (9.4(±0.6) kJ mol-1) has been ascribed to its stiff ligand system. In

contrast, the FeII complex based on the ligand bis(2-pyridylmethyl)amine (Figure 7; 15),

for example, can more easily accommodate such twisting, and its activation parameter is

correspondingly lower (2 kJ mol-1).18

(14) (15)

Figure 7. (14) [1,4,-(2´-pyridyl)2-7-(6´-R-2´-pyridyl)]-triazacyclononane. (15) bis(2-pyridylmethyl)amine.

The relevance of iron porphyrinate systems to the allosteric mechanism of

hemoglobin oxygenation has made their SCO species the subjects of repeated

investigation. In some cases, the relative stability of spin states of porphyrinate

complexes has been attributed to steric effects of the axial ligands. In the bis(2-

methylimidazole)(octaethylporphinato)iron(III) complex ([Fe(OEP)(2-MeIm)2]ClO4)

(Figure 8; 16), for example, the 2-MeIm ligand plane comes to within 22° of eclipsing the

nearby Fe–Npor bond, and the resulting congestion is thought to prevent the imidazole

from approaching the metal center closely enough to stabilize a low-spin state. The

12

orientation and corresponding high-spin state (µeff = 5.52 µB at room temperature) is

strictly a solid-state effect; in solution, where the axial ligands are free to rotate, SCO

behavior is exhibited. Interestingly, its solution behavior is similar to that of the related

[Fe(TPP)(2-MeIm)2]ClO4, but the latter complex is low spin in the solid state. The

crystal structure of the TPP complex reveals that the imidazole ligand is rotated farther

from the nearest Fe–Npor bond; the imidazole can then approach the metal more closely

and support its low-spin state.19 Related examples have been described elsewhere.20

(16)

Figure 8. (16) Bis(2-methylimidazole)(octaethylporphinato)iron(III).

The sometimes confounding effects of steric crowding and electron donation are

exemplified in a series of FeIII cyclamacetate complexes in which the axial ligands are

acetate and either fluoride or OFeCl3, and in which the cyclamate ring is either

unsubstituted or trimethyl substituted. Based on crystal structure data, DFT calculations

were conducted on a model compound (Figure 9; 17). When R = H, the complex is low

spin (S = 1/2); if R = Me, the complex is high spin (S = 5/2), in agreement with

13

experimental measurements. The reason for the difference was assigned to steric

crowding from the methyl groups (e.g., the crystal structure of the high-spin complex

reveals non-bonded hydrogen contacts as short as 2.23 Å), and to the electron-

withdrawing effects of the methyl groups on the amine nitrogens. Although the net result

is that the Fe–N bonds lengthen with methyl substitution (by 0.13 Å in the calculations),

thus weakening the ligand field, it was not possible to determine whether steric crowding

or electron withdrawal contributes more to the high-spin state.5 Solvation effects,

however, appear to be comparatively unimportant.

(17)

Figure 9. (17) FeIII cyclamacetate model complex.

Other multidentate ligands

The pyridine-containing branched chelating ligands tetrakis(2-pyridylmethyl)-1,2-

ethanediamine (tpen) (Figure 10; 18; R = H) and the closely related 6-methylpyridyl

substituted derivative (mtpen) (Figure 10; 18; R = Me) differ by only a single methyl

group on one arm. The FeII tpen derivative displays SCO behavior, in both solution and

the solid state, yet the mtpen analogue (19) is strictly high spin. Evidence from the X-ray

14

crystal structure was used to show that steric influence of the methyl group was enough

to prevent the approach of the pyridyl group to the distance (ca. 2.0 Å) required for a

low-spin complex; at 2.17 Å, the Fe–Npy distance will only support the high-spin state.21

(18) (19)

Figure 10. (18) R = H, tpen; R = Me, mtpen. (19) Fe[mtpen]2+.

A smoothly varying example of variation in SCO temperature as a response to

steric pressure is provided by the series of FeII compounds based on the hexadentate

ligand tris[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine (Figure 11; 20), where R is either H

or CH3 (Figure 11; 21).22 The complex with all R = H is low spin up to 400 K. When one

of the three R groups is methyl, the complex undergoes a low-spin to high-spin transition

at 380 K. With two and three methyl groups, the transition temperature drops to 290 K

and then 215 K, respectively. The increasing steric pressure from the methyl groups

lengthens and weakens the Fe–N interactions, which in turn disfavor the low-spin state.

15

(20) (21)

Figure 11. (20) Tris[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine. (21) Fe[tris[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine]2+

The competition that can exist between the donor and steric properties of a ligand

and their effect on magnetic properties is nicely illustrated in complexes of 2-

pyridinalpheylimine (Figure 12; 22), which can be tuned for the proportion of their high-

or low-spin states depending on the presence of methyl substituents. [FeL2(NCS)2] (R1,

R2, R3 = H) displays SCO behavior, but at 4.2 K, 60% of the complex is still in the high-

spin form. Addition of a methyl group to the ligand (R1 = Me) causes the resulting

complex to convert entirely to the low-spin state by 78 K; evidently the donor effect of

the methyl group overrides any extra congestion that may be generated around the metal

center. If the methyl group is added at R2 or at R1 and R2, however, the crowding around

the metal center overrides the inductive effects of the methyl group(s). Interestingly,

when methyl groups are present at R1 and R3, the complex is also high spin at all

temperatures, and Mössbauer spectra display a single quadrupole doublet, typical for

high-spin species. It is believed that the R3 methyl group sterically interacts with the

hydrogen on the imine carbon, causing twisting of the ligand and reducing its donor

ability.23

16

(22) Figure 12. (22) 2-pyridinalpheylimine model compound

Although certainly established, SCO in CoII systems has far fewer documented

examples than the corresponding FeII species. Steric crowding appears to be the reason

that the tris CoII complex dication with the 6-methyl pyridine-substituted ligand (Figure

13; 23) (R = Me) displays a magnetic moment of 3.50–4.31 µB over the temperature

range from 80–383 K, whereas the same complex with R = H cannot reach the high-spin

state under similar conditions (µeff = 2.41 µB at 385 K).24 Steric effects have also been

implicated in derivatives containing the ligands (Figure 13; 24) (R = t-Bu, i-Pr) and the

facially coordinating tripyridylamine (Figure 13; 25) (R = Me). In the latter, a spin

transition from µeff = 2.15 µB at 95 K to 3.82 µB at 373 K is observed when R = H; when

R = Me, however, the complex is strictly high spin.

(23) (24) (25)

Figure 13. Structures of the substituted pyridine ligands (23), (24), and (25).

17

Metallocenes

With relatively few exceptions, metallocenes are low-spin compounds, a

consequence of the strong field nature of the cyclopentadienyl (Cp) ligand. They are

characterized by a large HOMO–LUMO gap between the frontier nonbonding and

antibonding molecular orbitals. This is particularly true for 4th and 5th row transition

metals, with the result that 4d and 5d cyclopentadienyl compounds are exclusively low

spin. Even among first-row metallocenes, the ability to display variable spin states is

confined to those of manganese and to a much smaller extent, chromium.

Manganocenes

Manganocene ([MnCp2]) is an anomaly when compared to its neighboring

metallocenes; owing to its half-filled d electron shell, there is no ligand field stabilization

energy (LSFE), and a high-spin ground state (6A1g) is found at room temperature. The

high-spin preference is only 2.1 kJ mol-1,25 and although its solution magnetic moment is

5.5 µB at room temperature, it undergoes SCO at reduced temperatures (µeff = 1.99 µB at

193 K).26 These moments are relatively close to the spin-only values for 5 and 1 unpaired

electrons (5.92 µB and 1.73 µB, respectively).

Changing the substituents on the Cp ligands can modify the relative preference for

spin states in manganocenes. Addition of a single methyl group to each Cp ligand results

in a compound that exhibits a spin state equilibrium between two states at room

temperature.25 Further methylation of the Cp ligand can produce a completely low-spin

compound (µeff = 2.18 µB), as observed with decamethylmanganocene ([MnCp*2], Cp* =

C5Me5).27 An important structural difference between the high and low-spin manganocenes

18

is exhibited in their Mn–C distances. In the case of the high-spin [MnCp2], the avg. Mn–

C distance is 2.41 Å, which is considerably longer than that in [MnCp*2] (avg. of 2.11

Å). The short distance exists despite the increased steric bulk of the Cp* ligand, which in

the absence of a spin state change might be expected to lengthen the metal-

cyclopentadienyl separation.27

However, sufficient steric interactions can in certain cases override electronic

donor effects in manganocenes. For example, the isopropyl metallocene [M(Cp3i)2] (Cpni

= C5(iPr)nH5-n) displays SCO behavior; it is low spin at low temperature (1.89 µB at 5 K),

with Mn–C distances typical of the low-spin state (2.130(6) Å), but reaches a moment of

3.25 µB at 348 K, indicative of an incomplete spin state change.28 In contrast, [Mn(Cp4i)2]

(Figure 14; 26) is entirely high-spin (5.5 ± 0.1 µB) from room temperature down to 10

K.28 This is despite the presence of an additional electron donating i-Pr group on each

ring, which should help stabilize a low-spin compound. The increased steric bulk of the

Cp ligand instead generates considerable intramolecular strain, as demonstrated from the

displacements of the isopropyl methine carbons by up to 0.26 Å from the Cp ring plane.

This leads to a bent structure in the solid state (Cpcentroid–Mn–Cpcentroid = 167°) and

elongated Mn-C bonds (avg. = 2.42(2) Å), which are characteristic of high-spin

manganocenes.

19

(26)

Figure 14. (26) Octaisopropylmanganocene

The difference in spin state leads to a notable difference in the reactivity of the

two manganocenes. The SCO compound [Mn(Cp3i)2] reduces tetracyanoethylene

(TCNE) in acetonitrile at room temperature to form the [TCNE]•- radical anion. In

contrast, the high-spin [Mn(Cp4i)2] undergoes a tricyanovinylation reaction with TCNE to

form C5(i-Pr)4HC(CN)=C(CN)2.28

Trimethylsilyl and t-butyl substituted manganocenes show trends in magnetic

behavior that to some extent parallel those observed with the hexa- and octaisopropyl

manganocenes, although not always for the same reason.29 In the case of the

trimethylsilyl substituted manganocenes, the presence of single trimethylsilyl group on

each Cp ring produces a compound that is high spin from 150–300 K (µeff = 5.9 µB),

although the effective magnetic moment drops to ~5.3 µB at 100 K. Addition of a second

and third trimethylsilyl group to each Cp ring produces compounds that are completely

high spin at from 5–300 K (µeff ~5.9 µB). There is clearly intramolecular crowding in

some of the molecules; in [Mn{1,2,4-(Me3Si)3C5H2}2], the silicon atoms of the

20

trimethylsilyl groups are displaced from the ring plane by an avg. of 0.27 Å.

Trimethylsilyl groups on Cp rings are net electron-withdrawing substituents, however,

and this is undoubtedly the fundamental source of the high-spin states.

In contrast, both electronic and steric effects on magnetic behavior are clearly

observed with t-butyl substituted manganocenes. The singly substituted

[Mn{(Me3C)C5H4}2] is high spin at room temperature (µeff ~5.8 µB) but displays SCO

behavior, with an effective magnetic moment of ~2.2 µB near 175 K. The additional

electron donation from a second t-butyl group causes [Mn{1,3-(Me3C)2C5H3}2] to be low

spin at room temperature (µeff = 2.2–2.3 µB). Addition of a third t-butyl group to each Cp

ring, however, leaves [Mn{1,3,4-(Me3C)3C5H2}2] (Figure 15; 27) entirely high spin at all

temperatures, with a moment of 5.8-5.9 µB from 5–300 K. The steric strain provided by

the rings in 27 is apparent from the bent solid state structure (Cpcentroid–Mn–Cpcentroid =

169°), in which the quaternary carbon is displaced from the ring plane by 0.21 Å and the

Mn–C bond lengths range from 2.350(4) Å to 2.470(4) Å, typical for a high-spin

manganocene.

(27)

Figure 15. (27) [Mn{1,3,4-(Me3C)3C5H2}2].

21

Chromocenes

Using the value of the (ln[(2S+1)HS/(2S+1)LS]) ratio as a guide (see beginning of

Section 2), complexes containing CrII (ΔS = ln(5/3)) should be among the least likely to

display SCO behavior, and barring orbital symmetry effects (see Section 3),

organometallic compounds of CrII with π-bound ligands are almost always low-spin

species. For example, whereas [Mn(Cp3i)2] displays SCO behavior, the chromium

analogue [Cr(Cp3i)2] is low spin at all temperatures. [Cr(Cp4i)2] is a rare exception to this

rule and exhibits SCO behavior in the solid state (Figure 1), becoming high spin (µeff =

4.90 µB) at room temperature.30 In toluene solution at room temperature, however

[Cr(Cp4i)2] is low spin, reflecting the lack of cooperative effects from a solid state lattice.

Figure 16. SQUID magnetometry data for [Cr(Cp4i)2] showing its SCO behavior from S = 1 to S = 2.

Symmetry Effects on Magnetism in Coordination and Organometallic Complexes

Apart from their donor/acceptor differences and steric effects, the relative

orientation of ligands around a metal center can affect the spin state of a complex. The

situations in which this occurs vary, but most commonly it involves changes in the

22

overlap of ligand π orbitals and the metal d orbitals.

The orientation of ligands in coordination compounds such as six-coordinate FeIII

Schiff base and porphyrinate complexes is thought to affect the spin states of the metal

centers. An instructive example is provided by the imidazole ring alignments in FeIII

complexes of several quadridentate Schiff bases.31 The complex [Fe(L1)(HIm)2]ClO4

(Figure 17; 28) is high spin at room temperature (µeff = 5.89 µB); in the solid state, the

imidazole ligands are roughly parallel to each other (dihedral angle of 10.2°) and bisect

the O–Fe–N angles. In contrast, the two imidazole ligands in [NaFe(L2)(HIm)2(ClO4)2]

(Figure 17; 29) are twisted by 79° relative to each other, and are oriented along the N–

Fe–O diagonals of the equatorial ligand plane. This places them in a near optimum

arrangement for competent dπ-pπ Fe–L bonding, and arguably helps stabilize the low-spin

state that 29 displays from 4.2–300 K (µeff = 2.10 µB). Other examples in which axial

ligand orientation is associated with spin state differences are described elsewhere.20

(28) (29)

Figure 17. (28) [Fe(L1)(HIm)2]ClO4. (29) [NaFe(L2)(HIm)2(ClO4)2].

23

An extensive set of organometallic compounds that displays magnetic behavior

controlled by the orientation of the ligands is found among the bis(indenyl) complexes of

CrII. Despite the parallels that are sometimes drawn between the indenyl and Cp ligands,

such conformationally controlled magnetochemistry is not shared with metallocenes.

The rotational conformation of Cp ligands need not be considered when rationalizing

their interactions with d orbitals, nor when analyzing their effect on d-orbital energy

levels and splitting.32

By replacing the Cp ligand in sandwich complexes with the less symmetrical

indenyl anion (Figure 18), symmetry-induced effects can play a role in determining their

magnetic properties. Qualitative molecular orbital diagrams33 illustrate the difference in

the interactions between the π orbitals of the indenyl anion and the metal d orbitals in

staggered (Figure 19) and gauche (twisted) (Figure 20) forms of [CrInd2].

Figure 18. Indenyl ligand with numbering scheme

24

Figure 19. Qualitative molecular orbital diagram for bis(indenyl)chromium(II) with a staggered conformation.

Figure 20. Qualitative molecular orbital diagram for bis(indenyl)chromium(II) with a gauche conformation.

25

As can be seen in Figure 19, a centrosymmetric (staggered) geometry stabilizes a

high-spin state due to the inability of ungerade combinations of the indenyl π orbitals to

interact with the d orbitals of chromium. The HOMO of the complex is an antibonding

combination of a metal d orbital and π4, with the next three filled orbitals being primarily

metal-centered. The au and bu combinations of the π4 and π5 orbitals are nonbonding, and

the electrons in the ligand π3 orbitals display limited interaction with the metal 3d orbitals

owing to their relative energy differences.

When the indenyl ligands in an [MInd2] complex are rotated to a gauche

conformation (Figure 20), the molecular point group is lowered to C2. Greater mixing of

the d orbitals can now occur with the π-orbitals of the indenyl anion. The symmetric and

antisymmetric combinations of both the indenyl HOMO (π5-π5) and HOMO-1 (π4-π4)

orbitals are of the proper symmetry to mix with the metal dx2-y2, dz2, and dxy (A

symmetry) and dyz, dxz (B symmetry) orbitals. This is most clearly seen in the case of the

π4 orbitals, which combine with the d orbitals to form bonding orbitals C and D. The

corresponding antibonding combinations are raised far above the energy of a largely non-

bonding orbital, which has now become the HOMO. A similar effect occurs with the π5

orbitals.

Bis(indenyl)chromium(II) complexes with methylated ligands

Bis(indenyl)chromium(II) compounds have been prepared that display a variety

of spin state behaviors depending on the substitution of the indenyl ligand. The parent

unsubstituted bis(indenyl)chromium(II) is a diamagnetic dimer,34 but the addition of a

single methyl group to the 5-membered ring of the indenyl ligand leads to the isolation of

26

monomeric species that can have from 2 to 4 unpaired electrons depending on the

location of the methyl groups and the overall geometry of the molecule. Evidence for the

ability of a staggered bis(indenyl) geometry to stabilize a high-spin state is found in

[Cr(2-MeC9H6)2] (Figure 21; 31), in which the addition of the methyl group in the 2-

position leads to the isolation of a purple monomeric complex with a staggered

geometry.35 Magnetic data on 31 shows it to be high spin over all temperatures both in

solution (µeff > 4.5 µB) and in the solid state (4.3-4.4 µB above 25 K). The avg. Cr–C

bond for 31 is 2.308(7) Å, typical for high-spin bis(indenyl)CrII compounds.

Substitution in the 1-position of the indenyl ligand leads to a green monomeric

species, [Cr(1-MeC9H6)2], with an eclipsed structure in the solid state (Figure 21; 32).35

Magnetic susceptibility measurements indicate that 32 undergoes a slightly incomplete

spin transition from 2 to 4 unpaired electrons, starting with a magnetic moment of 2.87

µB at 20 K, close to the spin-only value for 2 unpaired electrons (2.83 µB). The moment

then increases to a value of 4.1 µB at 275 K. Solid 32 dissolves in toluene to yield a

purple solution, and is found to be high spin (µB > 4.6 µB) over the range from 185–275

K, likely due to the adoption of a staggered geometry in solution, as there are no crystal

packing effects to enforce an eclipsed structure. Further evidence of the spin transition

can be observed from crystal data, as the avg. Cr–C bond increases from 2.179(9) Å at

105 K (typical for low-spin bis(indenyl)Cr(II) complexes, which generally range from

2.18–2.22 Å) to 2.262(10) Å at 298 K.

27

(31) (32)

Figure 21. (31) Bis(2-methylindenyl)chromium(II) (staggered). (32) Bis(1-methylindenyl)chromium(II) (eclipsed).

Additional methylation of the front side of the indenyl ligand, as in [Cr(1,2,3-

Me3C9H4)2], leads to a compound that displays SCO in the solid state despite having a

staggered structure.36 The complex is low spin below 115 K (µeff = 2.7-3.0 µB), but the

effective magnetic moment continuously rises to 4.4 µB at 225 K, effectively reaching a

high-spin state. This SCO behavior is likely due to competition between the electron

donating groups on the indenyl ligand that help to stabilize a low-spin state and the

symmetry preference for a high-spin configuration. A crystal structure obtained for the

compound at 173 K, in the middle of the spin state transition, revealed an avg. Cr–C

bond distance of 2.239(11) Å, which is appropriately between the values characteristic of

low-spin and high-spin complexes for CrII.

The presence of methyl substitution on the benzo portion of the indenyl ligand has

been examined in the case of [Cr(4,7-Me2C9H5)2]. The monomeric compound has an

eclipsed conformation and displays SCO behavior, undergoing an incomplete transition

from 2 to 4 unpaired electrons over the temperature range from 110 K (3.1 µB) to 300 K

(4.0 µB).35 The avg. Cr–C distance in the compound is 2.18(1) Å at 173 K, which is

28

consistent with a low-spin CrII compound. In solution, the compound has a magnetic

moment of 3.4 µB at room temperature, reflecting a mostly low-spin compound at room

temperature. This suggests that regardless of its exact conformation in solution, the two

methyl groups on the benzo ring are enough to keep the compound low spin. Methyl

substitution on the 4,7 positions should strongly affect the energy of the HOMO (π5) and

HOMO-2 (π3) orbitals, and calculations indicate that the energy of the π3 orbital is raised

by roughly 0.3 eV relative to the unsubstituted anion.36 In such a condition, interaction

with the π4 orbital of the ligand is destabilizing if the molecule remains in the high-spin

state. The energy of the entire molecule can be lowered if it transitions to the low-spin

state.

The addition of a methyl group to the front side of the ring in addition to the two

benzo methyl groups leads to the formation of [Cr(2,4,7-Me3C9H4)2], which displays

SCO behavior in both the solid state and in solution but undergoes an incomplete

transition in both cases. This is likely caused by the presence of the two structural

conformers in the same unit cell with different magnetic properties (a partial unit cell is

given in Figure 22). Crystal structure determinations of the complex were obtained at

173 K and 293 K; at 173 K, the avg. Cr–C bond in the eclipsed conformer is 2.168(5) Å,

and is statistically indistinguishable from that in the staggered structure (2.172(4) Å).

Both of these values are consistent with low-spin CrII. At 273 K, the avg. Cr–C bond in

the eclipsed conformer is 2.187(9) Å (∆Cr-C = 0.019 Å) while that of the staggered

structure has lengthened to 2.227(3) Å (∆Cr-C = 0.055 Å). This asymmetrical lengthening

in co-crystallized, otherwise identical molecules provides unambiguous evidence for the

operation of relative ligand orientation on the metal spin state.

29

Figure 22. Partial unit cell of bis(2,4,7-trimethylindenyl)chromium(II) showing both staggered and eclipsed conformers.

Complete methylation of the benzo portion of the ligand in the cases of

[Cr(2,4,5,6,7-Me5C9H2)2] and [Cr(1,2,3,4,5,6,7-Me7C9)2] leads to monomeric compounds

that are nearly entirely low spin in the solid state despite their staggered geometries.33,37

The pentamethyl indenyl complex remains low spin up until 175 K (2.83-2.86 µB), and

then appears to begin a spin transition as the moment rises slightly to 3.1 µB by 275 K

(Figure 23). In solution, the pentamethyl complex shows no signs of SCO behavior from

242–293 K, maintaining a magnetic moment of 3.5 µB throughout. Its solid-state

structure reveals an avg. Cr–C bond length of 2.17(1) Å at 173 K, indicative of a low-

spin CrII center. The heptamethyl complex remains low spin at all measured

temperatures. The fact that these compounds exhibit a low-spin moment despite their

staggered geometries demonstrates that the effects of symmetry on spin state are not

absolute in the presence of sufficient electronic donation.

30

Figure 23. SQUID magnetometry data for methylated bis(indenyl)chromium compounds.

Bis(indenyl)chromium(II) complexes with bulkier substituents

By increasing the steric bulk of the substitution in the 1-position on the indenyl

ligand from a methyl group to a t-butyl, a staggered geometry will be preferred for steric

reasons. The monosubstituted alkyl [Cr(1-(t-Bu)C9H6)2] displays a high-spin state in

solution (µeff = 4.8 µB from room temperature down to 183 K).33 The avg. Cr–C bond

distance in the solid state is 2.32(2) Å, also consistent with a high-spin metal center.

The substitution of a trimethylsilyl group in the 1-position of each indenyl ligand

produces [Cr(1-(SiMe3)C9H6)2], whose magnetic properties mirror that of the

monosubstituted t-butyl complex. It is high spin at all temperatures, with an effective

magnetic moment of 4.9 µB in solution from room temperature down to 183 K, and a

moment of 4.1 µB in the solid state from room temperature down to 30 K (Figure 24).

31

Figure 24. SQUID magnetometry data for bis(indenyl)chromium(II) compounds with t-Bu and SiMe3 substitutions.

Addition of a second trimethylsilyl group in the 3-position of the ligand leads to

formation of [Cr(1,3-(SiMe3)2C9H5)2]; it has a gauche conformation that reduces

intramolecular crowding. With its lowered symmetry (ideally C2), the gauche

conformation favors a low-spin state, both in the solid state (µeff = 2.8–3.3 µB over the

range from 10-350 K) and in solution (µeff = 3.0–3.2 µB from 183-300 K). The solid-state

structure is also consistent with a low-spin CrII center (avg. Cr–C bond distance of

2.20(2) Å), despite the large amount of steric bulk on the indenyl ligand that causes the

trimethylsilyl groups to be displaced from the ring plane by 0.31 Å.

The analogous t-butyl complex [Cr(1,3-(t-Bu)2C9H5)2] (Figure 25; 33) is also

monomeric with a gauche conformation,33 and is low spin in the solid state with an

effective magnetic moment of 2.8 µB up to 120 K; it rises slightly to 3.4 µB by 275 K. In

solution 33 displays an incomplete SCO between 213 K (µeff = 2.9 µB) and 300 K (µeff =

3.6 µB), and changes color from green at 213 K to brick red at room temperature. The

solid state structure shows an avg. Cr–C bond distance of 2.22(2) Å, which is at the high

32

end of the range observed for low-spin CrII centers; it is nevertheless considerably shorter

than the 2.32(2) Å found in [Cr(1-(t-Bu)C9H6)2].

(33) (34)

Figure 25. (33) [Cr(1,3-(t-Bu)2C9H5)2]. (34) [Cr(1,3-(i-Pr)2C9H5)2].

The ability of symmetry constraints to influence spin states is also evident when

comparing the properties of 33 to its isopropyl analogue [Cr(1,3-(i-Pr)2C9H5)2] (Figure

25; 34). The reduced steric strain from the replacement of the t-butyl groups with

isopropyl groups leads to a molecule with a staggered geometry and approximate Ci

symmetry. Appropriately, 34 is high spin at all temperatures, with an effective magnetic

moment of 4.4-4.6 µB from 20-350 K in the solid state and 4.9 µB in solution at room

temperature.38

33

CHAPTER II

STRUCTURAL FEATURES OF ORGANOMANGANESE COMPOUNDS

Introduction

Compounds of manganese containing M–C bonds present challenges in synthesis

and characterization that slowed the development of their chemistry relative to that of

neighboring first row transition metals. There are many historical examples of this; for

example, the binary carbonyls Fe(CO)5 and Cr(CO)6 were reported in 1891 and

1926,39,40 respectively, whereas the parent carbonyl of manganese, Mn2(CO)10, was not

characterized until 1954 (from a reaction with a yield of 1%).41 Gilman reported without

details the synthesis of phenylmanganese iodide and diphenylmanganese in 1937,42,43 but

even this was almost two decades after Hein described the first of his

‘polyphenylchromium’ compounds (1919).44 Structural authentication of

organomanganese compounds was also slow in appearing; the polymeric solid state

structure of manganocene, {Cp2Mn}∞, for example, was not described until 1978,45 26

years after the sandwich structure of the monomeric ferrocene was confirmed

crystallographically.46 And although a route to pure diphenylmanganese was described in

1959,47 its structure determination by X-ray crystallography was first reported 50 years

later.48

There are several reasons for the experimental difficulties encountered in

organomanganese chemistry, including such basic issues as differences in the reactivity

of manganese halides prepared by various methods,41 the disparate outcomes of reactions

34

using different hydrocarbyl transfer agents (e.g., LiPh vs. MgPh2),47,49 and the changes in

reaction products from the presence of even trace amounts of polar solvents.48 In

addition, the high-spin d5 valence electron configuration found in many complexes of

MnII provides no ligand field stabilization energy, and these compounds display

appreciable ‘ionic’ character; i.e., higher kinetic lability and a broader variety of

stereochemistries than compounds of adjacent divalent metal ions. Useful comparisons

can in fact be made between complexes of MnII and those of MgII, stemming from the

similarities of their charge/size ratios (rMnII = 0.81 Å; rMgII = 0.86 Å).50,51 For compounds

of MnII, there is a correspondingly weaker correlation between solution and solid state

structures than is true for manganese species in other oxidation states. The discontinuity

of the properties of organomanganese(II) complexes relative to other first row

counterparts is such that they have been dubbed the ‘black sheep’ of the organometallic

world.52

Structural characterization of organomanganese complexes relies on the same

battery of techniques (e.g., optical, IR, microwave, NMR and ESR spectroscopy, kinetic

and electrochemical methods, mass spectrometric studies, and X-ray crystallography) that

are used for compounds of other metals. There are some considerations associated

specifically with manganese complexes that are outlined here.

Spectroscopic and Crystallographic Characterization

Nuclear Magnetic Resonance Spectroscopy

As with other organometallic compounds, both 1H and 13C NMR spectroscopy are

extensively used in the characterization of organomanganese compounds. The 55Mn

nucleus is quadrupolar (100% nat. abund., I = 5/2), however, meaning that even in

35

diamagnetic compounds the signal of atoms directly bound to the metal will typically be

broad and not well-resolved. This of course principally affects 13C NMR spectra, and can

interfere with the observation of intermolecular exchange processes. One way this has

been circumvented in the case of metal carbonyls is with the use of 17O NMR

spectroscopy, as 55Mn–17O coupling is not observed in Mn–CO linkages. In the case of

CH3Mn(CO)5, for example, only one broad resonance is observed for the carbonyl groups

in its 13C NMR spectrum;53 in the room temperature 17O NMR spectrum, however, two

resonances corresponding to 4 equatorial and 1 axial carbonyls are observed,

demonstrating that exchange is not occurring.54 Other uses of 17O NMR spectroscopy

have been found in the study of demetalation reactions and polymetallic complexes.55-58

Paramagnetic NMR (principally 1H and 13C) has been used in the study of various

organomanganese complexes,59,60 and in the case of manganocenes, it is possible to

observe mixtures of low- and high-spin species in solution.61,62 In many reports of

paramagnetic organomanganese complexes, however, NMR spectra are not reported, and

often it is not clear whether attempts were made to observe a signal. Studies with 55Mn

NMR spectroscopy are less common, and owing to the large quadrupole moment of

55Mn, resonances with line widths of several kHz can be encountered.63 A substantial

body of data has been accumulated, however,63-66 and DFT calculations have been used

with some success in correlating 55Mn NMR chemical shifts.67 Solid state 55Mn NMR

has only rarely been used in the study of organometallic complexes,68,69 but the technique

has been shown to be highly sensitive to the local environment of the manganese center,

and it may be a promising characterization tool when other methods such as X-ray

crystallography are not applicable.

36

X-ray Crystallography

By far the premier method for the determination of organomanganese structures

has been single crystal X-ray crystallography; powder diffraction has been used to a

much smaller extent.70 As with other areas of manganese chemistry with M–C bonds,

crystal structures were slow to appear; the first was for Mn2(CO)10 in 1957,71 and the

second not until 1963 (that of CpMn(CO)3,72 although preliminary details were released

in 1960).73 Since those early days, the number of crystallographically characterized

compounds has increased steadily, and the total now exceeds 3000. Such studies have

been critical to clarifying the nature of M–C bonding, and serve as the major focus of this

review. Despite its value in locating the positions of hydrogen atoms bound to metals,

the necessity for large crystals and the scarcity of appropriate radiation sources has meant

that neutron diffraction studies have rarely been reported for organomanganese

compounds.74-76

General Considerations for Manganese–Carbon Bonds

A summary of crystallographically established Mn–C and Mn–Mn bond lengths is

given in Table 1; the distributions are discussed in more detail below.

Mn–C Bonds. The distribution of manganese-carbon single bonds is centered at 1.84 Å,

with an esd of 0.10 Å (Figure 26); there is substantial tailing on the long end, out beyond

2.5 Å. It should be noted that metal-carbonyl bonds are by far the most common Mn–C

bond types, representing over 94% of the total. The length of terminal manganese–

carbonyl bonds is fairly tightly clustered around 1.81 Å (esd of 0.04 Å) and dominates

the distribution. Excluding terminal or bridging M–CO bonds, and terminal cyano

37

ligands, the average Mn–C bond length increases to 2.11 Å, although the resulting spread

is clearly multimodal (Figure 26). Many complexes containing isonitrile ligands are

found in the peak centered around 1.9 Å; many alkyls and aryls are found in the 2.1–2.2

Å range.

Table 1. Distribution of Mn–C and Mn–Mn Bonds in Organometallic Compounds

Bond Type Mean Length (Å) Range (Å)

Mn–C 1.84 1.6–2.6

Mn–C (without M–CO bonds) 2.11 1.7–2.5

Mn=C 1.87 1.7–2.1

Mn≡C 1.67 1.6–1.7

Mn–Mn 2.85 2.3–3.2

Mn=Mna 2.39

Mn≡Mnb 2.17

aOnly two compounds known. bOnly one compound known.

Figure 26. Spread in manganese-carbon single bond lengths; on the left, including M–CO bonds; on the right, with M–CO and M-cyano bonds omitted.

0

200�

400�

600�

800

1000�

1200�

1400�

1600�

1800�

2000�

2200�

2400�

2600�

2800

1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4

Num

ber

of In

stan

ces

Mn1C Bond Lengths (Å)

0�

5

10�

15�

20�

25�

30�

35�

40�

45

1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5

Num

ber

of In

stan

ces

Non-Carbonyl Mn5C Bond Lengths (Å)

38

Although there are crystal structure determinations that report Mn–C bonds

shorter than 1.70 Å, including some less than 1.50 Å,77,78 many such structures are

afflicted with disorder, or are room temperature studies in which the bond distances are

artificially shortened because of high thermal motion. This is especially true of those that

list Mn–C bonds of 1.60 Å or less, and such studies should be viewed with caution. At

the long end of the range (up to ~2.65 Å) are weak contacts that involve bridging ligands

and special electronic situations; examples are found in the semibridging carbonyl

Mn…C contact at 2.648 Å in the heterobimetallic complex CpMoMn(CO)3(µ-CO)(µ-η2-

pyS)(µ-η1-pyS) (Figure 27; 35)79 and the Mn…C3 distance in Mn2(CO)8[µ-η2-C3H3NEt2]

(Figure 27; 36) at 2.56 Å.80 Constrained geometries can also lead to long metal-carbon

bonds; the hemiporphyrazine (Figure 27; 37)81 displays average Mn–C distances of 2.481

Å and agostic C-H interactions with the metal. The η1-coordinated cyclopentadienyl

ligand in Cp2Mn{HN=C(NMe2)2}2 (Figure 27; 38) is at 2.356 Å,82 and among the longest

carbonyl alkyl bonds is that of (CO)5Mn–CH2CH=CHCOOPh (Figure 27; 39) at 2.214

Å.83

(35) (36) (37)

OC MnSMo

CO N

OC

OC

N

S

Mn MnOC

OC

OC

CO

OC COCOOC

C3N

N N

N

NN

N Mnpy

H

H

39

(38) (39)

Figure 27. Structures of selected organomanganese compounds exhibiting noteworthy Mn-C bond lengths.

Mn=C Bonds. The length of manganese-carbon double bonds averages to 1.87

Å, but this number is of limited significance because the distribution of bond distances is

at least bimodal (Figure 29). The most clearly defined maximum, centered at 1.77 Å and

extending from 1.68 Å (found in (40); Figure 28) to about 1.81 Å, consists exclusively of

conjugated Mn=C=C units (e.g., vinylidenes, diylidenes). Only a few such species are

found at longer lengths (e.g., in (41; Figure 28), at 1.872 Å). The longer bonds have

apparent maxima at ca. 1.89 Å and 1.96 Å, although the compounds are not cleanly

separated into defined structural fragments. In general, however, the longest bonds are

found in complexes that contain multiple ligands with strong trans influence; especially

common are those with 4 CO ligands (e.g., 2.038 Å in 42; Figure 28)84 or (CO)3/(PR3)2

ligands (e.g., 2.004 Å in 43; Figure 28).85 The middle range of distances is dominated by

complexes containing the more weakly donating CpMn(CO)2 or CpMn(CO)PR3

fragments. It is clear that the M=C bond length is highly context-specific.

Mn

HN

NH

NMe2

NMe2

NMe2

Me2N MnCO

OC

CO

CO

OC

OPh

O

40

(40) (41) (42) (43)

Figure 28. Structures of selected organomanganese compounds exhibiting noteworthy Mn=C bond lengths.

Figure 29. Spread in manganese-carbon double bond lengths.

Mn≡C Bonds. The distribution of manganese-carbon triple bond lengths is

grouped around 1.67 Å; both the shortest known example,

[(MeCp)(dmpe)Mn≡CCH2CH2C≡Mn(dmpe)(MeCp)][PF6]2, (Figure 30; 44)86 and the

longest ([(MeCp)(dmpe)Mn≡C–C≡Mn(dmpe)(MeCp)][PF6]2) (1.734 Å) (Figure 30; 45)87

are dicationic, dinuclear complexes with MnIII centers. Two independent molecules are

Mn=C=C

OCOC

H

MnP

P

PPMnC C Mn

OC

OC O

CO

C

CO

Ph

MnPh3P

OC PPh3

CO

C

CO

NH

Ph +

0

2

4

6

8

10

12

14

16

18

20

22

24

26

1.70 1.75 1.80 1.85 1.90 1.95 2.00 2.05 2.10

Num

ber

of In

stan

ces

Mn=C Bond Lengths (Å)

41

found in the unit cell of (44), with Mn≡C bonds of 1.638 Å and 1.653 Å, which indicates

the amount of variation that can ascribed to packing forces alone.

(44) (45)

Figure 30. Structures of selected organomanganese compounds exhibiting noteworthy Mn≡C bond lengths.

Mono(cyclopentadienyl) compounds

The largest class of cyclopentadienyl manganese compounds is the cymantrenes

(Cp´Mn(CO)3) and their derivatives. These MnI compounds are 18e– species that are

extraordinarily stable and have classic three-legged piano stool geometry. The

Cp´Mn(CO)3 unit can also serve as an organometallic substituent on an otherwise

inorganic complex (Figure 31; 46); there are more than 230 crystallographically

characterized molecules for which such units (or closely related species such as

(indenyl)Mn(CO)3) are the only organometallic fragment. A related and even larger class

of structurally authenticated molecules (approximately 320 examples) consists of those in

which the cyclopentadienyl manganese dicarbonyl fragment, –MnCp(CO)2, is a

substituent on a complex (Figure 31; 47); the 16e– fragment (Cym´) is isolobal with

singlet methylene (:CH2) and the methyl cation (CH3+). In both classes of compounds,

the structural features involving the metal do not vary greatly.

Mn CP

P

PPC Mn

2+Mn CP

P

Ph

Ph

PPC Mn

2+

42

(46) (47)

Figure 31. Cymantrene as an organometallic substituent (46) and as 16e– fragment bound to a metal (47).

As mentioned above, (CpMn(CO)2) is a 16e– unit capable of accepting 2e–

ligands. Likewise, the CpMn subfragment itself is a 12e– moiety capable of coordinating

three 2e- donor ligands. In addition to carbonyls, various other donor ligands such as

phosphines, nitrosyls, isonitriles, and carbenes can coordinate to the Mn center to yield

cymantrene-like compounds CpMn(CO)3-xLx (x = 0–3). Of these carbonyl replacements,

phosphines are by far the most common, but are usually only structurally interesting as

sources of steric bulk.

In nearly all cymantrene-like compounds (CpMnL3), the Mn-Cp interaction and

overall geometry is relatively unchanged from the basic three-legged piano stool

configuration. Examples of this include (MeCp)Mn(CO)(PPh3)2 (Figure 32; 48)88 and

(MeCp)Mn(CNBPh3)(P(OPh)3)(NO) (Figure 32; 49).89 In 48, the average Mn–C(Cp)

bond length is 2.150 Å, and the Mn–C(O) bond is 1.749 Å, both very near the averages

observed in cymantrenes. In 49, the non-Cp ligands display interligand angles closer to

90° rather than the 109.5° expected for an ideal tetrahedral arrangement. Such angular

compression is typical for CpMnL3 complexes. The average Mn–C(Cp) distance is

unexceptional at 2.147 Å; the Mn-P bond of 2.213 Å, the Mn–C≡N bond length of 1.929

Å, and the C-N distance of 1.142 Å compare favorably to the distances in other CpMnL3

complexes, where the averages are 2.222, 1.920 and 1.155 Å, respectively.

MnOC CO

CO

LnM

43

(48) (49)

Figure 32. Solid state structures of (48) and (49).

The average Mn-C(Cp) distance for derivatives of cymantrene that contain either

one or no carbonyls is 2.156 Å, which is nearly identical to that found in with the Cym´

fragment itself (2.145 Å). There exist complexes that display deviations from these

averages, but regardless of the donor ligands that replace CO, none stray more than 0.1 Å

from the mean. Large deviations in the Mn-Cp interaction are only observed when the

compound is actually no longer that of the classic (η5-Cp)MnIL3 type, such as when the

cyclopentadienyl ligand is protonated to generate 5-exo-(MeCp)Mn0(CO)(NO)(PPh3)

(Figure 33; 50),90,91 or when a MnII center is present, such as in

(MeCp)(tmeda)MnII(C≡CPh) (Figure 33; 51).92

44

(50) (51)


Compound 50 is one of two products isolated from the reaction of

[CpMn(CO)(NO)(PPh3)]PF6 with LiCH3 and NaBH4; the Cp ligand is methylated by the

alkyl lithium reagent. The geometry around the Mn is roughly tetrahedral with slightly

distorted L-M-L bond angles (L ≠ Cp) that range from 93.9° to 102.8°. This is similar to

ranges observed in most cymantrene-like compounds that display the classic piano stool

structure; however, the protonation of the Cp ligand causes the carbon on the ring bound

to the methyl group (C1) to shift upward from the C5 ring plane by 0.53 Å, and the plane

created by C2, C3, C4 and C5 forms an angle of 147° with the plane created by C1, C2,

and C5. The result is a complex with an η4-coordinated cyclopentadiene ligand (Mn–C =

2.126 (avg.)); the Mn-C1(Cp) distance of 2.692 Å is non-bonding. Besides being a

unique derivative of cymantrene, (50) also represents a rare example of a formally Mn0

organometallic complex (other than those for which M–C interactions involve only

carbonyl ligands) that has been structurally authenticated.

45

Compound (51) was prepared by the reaction of (MeCp)2Mn(tmeda) with

PhC≡CH or PhC≡CSnMe3 in THF at room temperature, resulting in the displacement of

a MeCp ligand by the acetylene. The geometry of the ligands around Mn in (51) is

similar to that of many cymantrene-type compounds with a near tetrahedral arrangement

of the ligands, but the bond lengths are considerably different. The average Mn-C(Cp)

bond length of 2.514 Å is considerably longer than those for cymantrene derivatives; this

is a consequence of the high spin MnII metal center, which typically supports bonds that

are elongated in comparison to those in MnI compounds. The bond length differences are

similar to those observed in high- and low-spin manganocenes.

The gap in bond lengths due to oxidation and spin state in

mono(cyclopentadienyl)manganese complexes is evident in Figure 67 below, where all

compounds with a Mn-C(Cp) distance of less than 2.24 Å are either MnI species or low

spin (S = 1/2) MnII. There are also a much larger number of CpMnI complexes known

owing to the fact that MnI offers ligand field stabilization to form stronger metal–ligand

bonds.

Figure 34. Spread in Mn-C(Cp) distances in mono(Cp) manganese complexes.

46

Pi-bound systems

Other than the CpMn(CO)2 fragment, the first example of a CpMn complex

bound to a multihapto hydrocarbyl complex was (η5-MeCp)Mn(η6-7-exo-

phenylcyclohepta-1,3,5-triene) (Figure 35; 52)93. The compound was synthesized by

irradiating a mixture of (MeCp)Mn(CO)3 and 7-phenylcyclohepta-1,3,5-triene with UV

light to produce both the endo and exo isomers; a crystal structure was obtained for the

exo species. The two rings are parallel (Figure 35), and the average Mn-C bond lengths

of 2.123 Å for the cyclopentadienyl and 2.101 for the cycloheptatriene ligand are in the

range expected for MnI complexes.

Figure 35. Solid state structure of (52).

A set of similar sandwich complexes 53, 54, 55 was synthesized by the same

method of irradiating a cymantrene in the presence of cyclooctatetraenes (COT) to

produce Mn(η5-C5R4)(η6-C8X8) (R = H in (Figure 36; 54), and Me in (Figure 36; 53) and

(Figure 36; 55); X = F in 54 and 55, and H in 53). The complexes are structurally

47

analogous, which is somewhat surprising given the enhanced stability of the

perfluorinated species both thermally and in air. Metallotropic shifts can be observed

with NMR spectroscopy for the nonfluorinated compound, but neither perfluorinated

species displays fluxional behavior in their 19F NMR spectra.

(53) (54) (55)

Figure 36. Solid state structure of (53) and analogous structures for (54) and (55).

CpMn(C6H5R) compounds can be prepared by the reaction of MnCl2 and one

equivalent of NaCp to produce the mono(cyclopentadienyl) manganese chloride that can

then be further treated with phenylmagnesium bromide in THF to produce a mixture of

CpMn(C6H6) (56), CpMn(C6H5-Ph) (Figure 37; 57), and biphenyl.94 The structures of

(56) and (57) were both determined with X-ray crystallography, which revealed a large

amount of disorder in (56) due to the interchangeability of Cp and benzene in the

complex. The structure of (57) demonstrates that the average Mn-C distance to the

benzene is shorter than that to the cyclopentadienyl ligand (2.106 Å and 2.124 Å,

respectively).

48

(57)


Other mono(cyclopentadienyl) complexes

Photolysis of CpMnL3-xL´x (x = 0–3; L = CO; L´ = PR3) complexes in the

presence of silanes can result in the coordination of Mn to the silane or to a Si-H bond on

the silane in the form of a three-center two-electron bond.75,95,96 Stronger electron

donating groups on coordinated phosphines, or the presence of two coordinated

phosphines and no carbonyls, helps to facilitate Si-H bond cleavage and the formation of

MnIII silyl hydride complexes, as in CpMn(dmpe)(H)(SiHPh2) (Figure 38; 58).96

Although the hydrogen atoms could not be located in the X-ray structure, the geometry

around the Mn and silicon atoms provides a strong argument for the formation of a

manganese hydride. The coordination around the Mn appears to be that of a 4-legged

piano stool with one of the legs missing where the hydrogen atom would be. This is

evidenced by the large difference in Si-Mn-P bond angles, one of which is 86.4° while

the other is 115.8°.

Without the presence of the extra phosphine ligand in place of CO, or the electron

withdrawing groups on the phosphine, incomplete oxidative addition during the

photolysis reactions can result in the formation of three-center two-electron bonds, as in

49

the compound (MeCp)Mn(CO)(PMe3)(H)(SiHPh2) (Figure 38; 59).75 A neutron

diffraction study confirmed the locations of the hydrogen atoms and the appropriateness

of the delocalized bonding description.97

(58) (59)


Despite the vast amount of chemistry known for complexes of the form

[CpMnLx], there are relatively few Mn compounds of the form [CpMnLyX] for

comparison. Some early examples of these types of complexes were dimeric

CpMn(halide) complexes with coordinated bases. These compounds can be prepared by

allowing MnX2 (X = Cl, Br, I) to react with [MeCp]– in the presence of a coordinating

base such as triethylphosphine.98 The resulting complexes are dimeric with bridging

halides and a pseudotetrahedral geometry around the Mn centers, as observed in

[CpMnCl(PEt2)]2 (Figure 39; 60). The most striking difference between these

compounds and those of the type CpMnLx is in the Mn-C and Mn-P distances. The

average Mn-C(Cp) bond length in (60) is 2.484 Å, considerably longer than any other

Mn-C bond lengths mentioned in this section, most of which are less than 2.2 Å. The

50

Mn-P bond length of 2.567 Å is also considerably longer than the average Mn-P bond in

cymantrene-like compounds, where the average is only 2.22 Å. This may seem strange

given that the manganese centers are not sterically crowded or coordinatively saturated,

but makes sense when you consider we are now looking at a MnII species that is high

spin. The 5 unpaired electrons distributed throughout the d orbitals prevent any ligand

field stabilization, and lead to longer bonds. The bromine and iodine analogs of (60)

have also been crystallographically characterized and are isostructural in their geometries

and Mn-C and Mn-P bond distances.


Manganocenes and related compounds

Manganocenes

In comparison to the metallocenes of other first row transition metals,

manganocenes are unique in that they can adopt either a high (S = 5/2) or low (S = 1/2)

spin state based on the steric and electronic effects of the substituent(s) on the

cyclopentadienyl ligand. The availability of two potential spin states produces distinct

51

structural characteristics with respect to Mn–C distances. Manganocenes with a S = 5/2

spin state possess longer M–C bonds than are typically seen for metallocenes, and with

only a few exceptions are usually in the range 2.30–2.52 Å. The compounds at the short

end of this range are typically triscyclopentadienyl manganese compounds or

manganocenium ions. The bulk of unsolvated, substituted manganocenes display Mn–C

bond lengths of 2.35-2.42 Å. In contrast, low spin compounds have considerably shorter

Mn-C bonds that range from 2.09-2.25 Å. The histogram in Figure 40 illustrates the

sharp division between high- and low-spin manganocenes; there are no known Mn-C

distances in the range from 2.25–2.31 Å.

Figure 40. Spread of Mn-C distances in Cp2Mn complexes.

These compounds are generally prepared by the salt metathesis reaction of MnBr2

and the sodium or potassium salt of the desired substituted cyclopentadienyl ring

(Equation 1).29,99

52

MnX2 + 2 MCp → MnCp2 + 2 MX (X = Cl, Br, I ; M = K, Na) (eq. 1)

Manganocene, bis(cyclopentadienyl)manganese(II) (Figure 41; 61) was not

crystallographically characterized until 1978,45 a consequence of its polymeric nature and

the difficulty of obtaining suitable crystals.100 Unlike other first row metallocenes, which

have simple sandwich structures with parallel Cp rings, each Mn center in the

unsubstituted manganocene is coordinated to 3 cyclopentadienyl ligands. One ligand is

terminally bound in an η5 fashion, with an average Mn-C bond distance of 2.411 Å. Each

non-terminal Cp ligand is bridging between two Mn centers, with η1-coordination to one

Mn and η2-coordination to the other Mn; this forms an infinite polymeric structure. The

average Mn–C bond lengths are 2.441 Å and 2.438 Å for the η1- and η2-coordinated Mn–

Cp interactions, respectively. The Mn…Mn separation is relatively large at 5.38 Å. The

compound has a high spin ground state (6A1g) with a magnetic moment of 5.97 µB at 19

ºC, and displays antiferromagnetic behavior as a crystalline solid, the coupling arising

from interactions between the polymeric chains.100


53

The presence of a methyl group on each of the Cp ligands in 1,1´-

dimethylmanganocene (Figure 42; 62) produces a classic sandwich structure with two

differing geometries, depending on the high- or low-spin state of the MnII center.101 Both

of these structures were resolved using gas phase electron diffraction;102 the structural

information supported previously acquired magnetic data that indicated that the two

species were in a spin-state equilibrium at room temperature.25 The high spin species

exhibits an average Mn–C bond length of 2.433 Å, whereas the low-spin species displays

an average of 2.144 Å. The large difference is driven by the ligand field stabilization

energy and stronger covalent interaction present in the low spin species.

Figure 42. Gas-phase structure of dimethylmanganocene (62).

Decamethylmanganocene (Figure 43; 63) is also a monomeric sandwich complex,

but it is completely low spin at all temperatures.103 It has an average Mn-C bond length

of 2.112 Å, considerably shorter than the Mn-C distances in the high-spin form of the

parent manganocene, but consistent with the superior donor properties of the Cp* ring

compared to unsubstituted Cp.

54

Figure 43. Solid state structure of decamethylmanganocene (63).

In general, the electronic properties of the cyclopentadienyl rings have a greater

effect on the structures of substituted manganocenes than do possible steric effects

provided by the ligands. The spin state of the complexes is usually determined by the

donor abilities of the Cp ligands; more electron-donating groups favor the low spin state,

even if the rings are somewhat more bulky (e.g., Cp* vs. Cp). There is a point, however,

at which steric strain can overcome the donor properties of the Cp ligands by limiting the

approach of the rings to the metal center. Examples of this and descriptions of both

structures and magnetic properties for substituted manganocenes are discussed in detail in

Chapter I.

The presence of coordinated solvents can strongly influence manganocene

structures. For example, the polymeric structure of (61) can be disrupted by THF to yield

the monomeric complex Cp2Mn(thf) (Figure 44; 64).104 There are now only two Cp rings

coordinated to the Mn center, both in an η5 fashion. The complex is high spin with a

magnetic moment of 5.84 µB at 20 ºC in the solid state and an average Mn-C distance of

2.462 Å, which is typical for a high spin manganocene. The Cp rings are bent at an angle

of 138.1º owing to the steric congestion around the Mn center caused by the coordinated

55

THF. The relatively long Mn-O bond of 2.226 Å is similar to that in other MnII THF

complexes and suggests a mostly ionic interaction.

Figure 44. Solid state structure of THF solvated manganocene (64).

Other related structures can be obtained by allowing Cp2Mn to react with neutral

coordinating ligands, such as phosphines or amines, at room temperature in an organic

solvent. Cp2Mn(PMe3) (Figure 45; 65), Cp2Mn(PPh2Me) (Figure 45; 66), Cp2Mn(dmpe)

(Figure 46; 67), and (MeCp)2Mn(dmpe) (Figure 46; 68) were all prepared using this

method.87,105 Both (65) and (66) are similar to (64) in that the Cp rings are coordinated in

an η5 manner and the rings are bent to give an almost trigonal planar arrangement around

the manganese, with Cp(centroid)–Mn–Cp(centroid) bond angles of 142.3º in (65) and

142.1º in (66). The C(centroid)–Mn–P bond angles are 108.1º and 109.6º in (65) and

110.6º and 106.8º in (66), making the sum of the C(centroid)–Mn–Cp(centroid) and

Cp(centroid)–Mn–P bond angles (360º for (65) and 359.5 for (66)) that expected for a

trigonal planar geometry around Mn. The average Mn–C bond distances of >2.5 Å are

slightly longer than that of normal high spin manganocenes, but this is likely a

consequence of the added bulk on the phosphine groups preventing the Cp rings from

approaching the metal center any more closely.

56

(65) (66)

Figure 45. Structures of phosphine adducts of manganocene (65) and (66).

In the case of (67), a pseudotetrahedral geometry with C2 symmetry is generated

between the two Cp centroids and the two 2 phosphorus atoms. The steric bulk of the

coordinating ligand is such that the Cp–Mn interaction has a tilt angle (τ) of 7.3º,

meaning that while the Mn atom is still nearly centered above the ring in an apparent η5

manner, the Mn–C distances vary greatly (2.492–2.742 Å). The Mn–Cp(centroid)

distance is also relatively long at 2.334 Å, again due to the bulk of the dmpe ligand.

Some of this lengthening could also stem from electronic effects, as the complex is

formally a 21e– species; it is consequently unsurprising that similarly bulky, yet stronger

coordinating bases can cause ring slippage. Addition of a methyl substituent to each of

the Cp rings to produce (68) is enough to cause the slippage of one ring to an η2-

coordination. Ring slippage is also observed when Cp2Mn is allowed to react with

TMEDA and bulky N-heterocyclic carbenes. Reaction with TMEDA to produce

(C5H5)2Mn(tmeda) results in the slippage of one ring to an η1-mode while the other

remains bound in an η5 fashion.106 The bulky N-heterocyclic carbenes 1,3-bis(2,6-

dimethyl-4-bromophenyl)-imidazol-2-ylidene and 1,3-dimesitylimidazol-2-ylidene have

also been found to react with Cp2Mn to give similarly slipped species, in which neither

ring remains coordinated in an η5 manner.107 Reaction of manganocene with the less

bulky tetramethylimidazol-2-ylidene (Figure 46; 69) yields (η1-C5H5)(η2-C5H5)Mn(69)2

57

(Figure 46; 70), a complex with distorted tetrahedral geometry. The latter is unique in

comparison to cobaltocene, chromocene, and nickelocene, all of which react with (69) to

give ion pair species of the form [(η5-C5H5)Mn(69)2]+[(C5H5)]–.108

(67) (68) (69) (70)

Figure 46. Structures of phosphine and carbene adducts of manganocenes (67)-(70).

There are only 9 known examples of manganocenium ions ([Cp´2Mn]+) that have

been crystallographically characterized, all of which are in charge-transfer (CT) salts

featuring (63) as the electron donor. The electron acceptor in each of the CT salts is

planar in structure and most are of the metal-dichalcogolene variety,109,110 although some

contain purely organic acceptors such as 7,7,8,8-tetracyano-p-quinodimethanide

(TCNQ)111. Structurally speaking, the [Cp*2Mn]+ cation is very similar to low spin

manganocene, as the Mn-C distances are all in the range of 2.08-2.15 Å. This is at the

short end of the Mn-C distance range for low spin manganocenes, but reflects the

presence of the more highly charged MnIII centers in the cations. The only difference

between the crystallographically characterized [Cp*2Mn]+ ions is that not all of the

cations have the staggered ring structure found in (63). Instead, many of the CT salts

58

feature an eclipsed ring structure for the [Cp*2Mn]+ cation, a result likely due to the

packing effects of the charge transfer salt upon crystallization. The first of these charge-

transfer compounds was made by treating (63) with TCNQ to produce the CT salt

[Cp*2Mn]+[TCNQ]– (Figure 47; 71), which is a bulk ferromagnet with a Curie

temperature of 6.2 K and coercive field of 3.6 x 103 gauss.111 More recent efforts to

synthesize ferromagnetically ordered molecular charge-transfer salts have used metal-

dithiolate or diselenolate acceptors, such as decamethylmanganocenium

bis[bis(trifluoromethyl)ethylene diselenolato]metalate(III) (M = Ni (Figure 47, 72),

Pt).112

(71) (72)

Figure 47. Schematics for the CT salts (71) and (72).

Metal triscyclopentadienyl anions ([Cp´3M]–) are relatively rare; the first known

transition metal examples (and the first to involve paramagnetic metal centers) were

synthesized with MnII.113 The earliest versions were prepared in 2001 and made from the

reaction of Cp2Mn with CpK or Cp2Mg in a solution of THF. The structure of [(η2-

Cp)3MnK•1.5(thf)] (Figure 48; 73) features three η2-bound Cp ligands coordinating to

each MnII atom in a paddlewheel arrangement, which is then linked to other [Cp3Mn]–

anions by cation-π bonds between the potassium cation and the Cp ligands of neighboring

anions.113 This allows for the formation of cyclic [(η2-Cp)3MnK]3, which branches in

59

two dimensions to form a honeycomb sheet structure. The end result is a layered

structure similar to graphite, in which adjacent sheets are staggered in respect to one

another, with a large interlayer distance of ~9.5 Å. Despite considerable crystallographic

disorder from the presence of both right- and left-handed propeller-like arrangements, the

Mn–C distances can be determined to exist in the range of 2.36-2.41 Å, similar to the

distances commonly observed for high spin manganocenes. The range of Mn–C

distances (2.351-2.392 Å) in the ion-separated complex [(η2-Cp)3Mn]2[Mg(thf)6] (Figure

48; 74) are essentially identical to those of (73).113 It is believed that the Cp rings all

coordinate in an η2 manner in these types of complexes to avoid unfavorable electronic

arrangements, as three η5-coordinated rings would lead to a formal electron count of 23e–

; with all of the rings η2-coordinated, the anions are formally 14e– species. Magnetic

measurements of both (73) and (74) demonstrate that the compounds that are in a spin

equilibrium favoring mostly the high spin state (µeff = 4.8 µB) at room temperature; both

display decreases in the moment as the temperature is lowered. The fact the compounds

are mostly high spin at room temperature is also consistent with their Mn-C distances.

(81) (82)

Figure 48. Structures of triscyclopentadienyl manganate anions (81) and (82).

60

Several additional triscyclopentadienyl manganate(II) anions have been isolated

and structurally characterized.87,114,115 All of them possess a similar same paddlewheel

structure with three cyclopentadienyl rings η2-bound to the Mn center. Not all of them

possess the 3-dimensional layered structure of (73), but the immediate environment

around the manganese centers is nearly identical.

Bis(indenyl) Manganese Complexes and Other Bis(Cyclopentadienyl) Derivatives

The indenyl ligand [C9H7]– is often considered an analogue of the

cyclopentadienyl anion, in that both are 6-electron donors to metals and both can be

functionalized to fit specific purposes. Although in many cases the indenyl ligand can

replace cyclopentadienyl in a complex without materially changing the structure and

reactivity, there are instances in transition metal complexes where the “indenyl effect”

(the ability of the indenyl ligand to easily slip from η5 η3 η5 coordination) can help

enhance catalytic properties in transition metal complexes (Figure 49).

Figure 49. Rearrangements of the “indenyl effect”.

In contrast to their first row transition metal counterparts containing V,101 Cr,116

and Fe–Ni,117 many decades separated the appearance of bis(indenyl) complexes of MnII

from the corresponding manganocenes. The first bis(indenyl)manganese(II) compounds

were synthesized by allowing high purity anhydrous MnCl2 to react with potassium

indenide salts in THF.118 One of the most noticeable features of these compounds is the

61

flexibility found for the Mn-indenyl interaction. This was evident during the attempted

synthesis of the parent bis(indenyl)manganese,112 which produced a THF solvate (76); the

coordinated THF could not be removed by heating or vacuum.118 The two indenyl

ligands and the two THF molecules in (76) are arranged in a distorted tetrahedral fashion

around the Mn center, with one indenyl ring coordinated in an η1 fashion while the other

is η3-coordinated (Figure 97); magnetic measurements indicate that the compound is high

spin. The Mn–C bond length for the η1-coordinated indenyl is 2.222 Å to the carbon in

the C1 position of the indene (75), which is longer than the typical Mn-C bond for low

spin manganocenes, but is reasonable for a high-spin complex. The η3-coordinated ring

displays Mn–C distances ranging from 2.344 to 2.550 Å for the C1-C3 carbons on the

indenyl ligand, whereas the bridgehead carbons display Mn-C separations of over 2.8 Å.

The C–C distances in the two indenyl ligands show a noticeable difference based on their

coordination mode. For the η3-bound ring, the C–C distances on the 5-membered ring all

range from 1.41-1.44 Å, which is typical for a mostly delocalized cyclopentadienyl or

indenyl ligand. In contrast, the η1-bound ring has C–C bonds that range from 1.38-1.45

Å, with the two bonds near the carbon bound to Mn at 1.44 and 1.45 Å in length, while

the C2–C3 bond on the indenyl is 1.38 Å. This indicates a moderate localization of a

double bond between the C2 and C3 carbons.

62

(75) (76)

Figure 50. Numbering scheme for the indene ligand (75); Solid State structure of THF solvated bis(indenyl)manganese (76).

Unsolvated sandwich structures are found when sufficient bulk is added to the

indenyl ligand to prevent THF coordination. In the case of bis[2-

(trimethylsilyl)indenyl]manganese(II) (Figure 51; 77), the result is a monomeric

sandwich compound with η5-bound rings in a staggered geometry.118 The average Mn-C

bond distance of 2.409 Å is similar to, but slightly longer than, that of typical high spin

manganocenes. The rings can be considered to be η5-bound despite a noticeable amount

of slippage (ΔMn-C = 0.14 Å); similar displacements are encountered for

bis(indenyl)chromium complexes,119,120 and the η3-coordinated rings in

bis(indenyl)nickel have a much larger ring slip parameter (ΔNi-C = 0.44 Å).117 Bis(1,3-

diisopropylindenyl)manganese (Figure 51; 78) has a staggered monomeric structure, and

has an approximate average Mn-C bond distance of 2.4 Å.118

63

(77) (78)

Figure 51. Solid state structures for bis(2-trymethylsilylindenyl)manganese (85) and bis(1,3-diisopropylindenyl)manganese (86).

Addition of a second trimethylsilyl group to the indenyl ligand to produce bis[1,3-

bis(trimethylsilyl)indenyl]manganese(II) (Figure 52; 79) results in a complex that is

monomeric with a near gauche conformation (twist angle of 83.7º from eclipsed), and

that is similar to the analogous compounds for Cr119 and Fe.118,121-123 The rings possess

slightly distorted η5-coordination, with an average Mn–C distance of 2.42 Å and a ring

slip parameter (ΔMn-C = 0.12 Å) close to that found for (77). The overall structure is

slightly bent, with an angle between the C5 rings on the indenyl ligands of 5.1º, which is

significantly less than its Cr counterpart (11.5º) and slightly less than in the Fe analogue

(5.8º). The long Mn-C distance in (79) helps to reduce much of the steric impact of the

trimethylsilyl groups. The lowered steric strain can be gauged by the displacement of the

silicon atom from C5 ring plane of the indenyl ligand; the average displacement is 0.22 Å

for (87), while it is 0.31 Å and 0.38 Å in Cr and Fe, respectively.

64

Figure 54. Solid state structure of bis(1,3-bistrimethylsilylindenyl)manganese (87).

65

CHAPTER III

SYNTHESES AND STRUCTURES OF SUBSTITUTED BIS(INDENYL)MANGANESE(II) COMPLEXES

Introduction

As discussed previously at the end of Chapter II, the π indenyl anion [C9H7]− is

often considered a close analogue of the cyclopentadienyl anion [Cp]−. Both indenyl and

cyclopentadienyl ligands are readily functionalized, and their complexes have found uses

in a range of important applications, including polymerization and hydrosilylation

chemistry.124-132 Many of these properties, particularly those for catalysis, are often

enhanced in the case of the indenyl compounds due to the previously mentioned indenyl

effect.

Differences between indenyl and cyclopentadienyl ligands are also evident in the

first-row transition metal sandwich complexes L2M; the structures and properties of

(C9H7)2M (M = V133, Cr134, Fe–Ni135) compounds diverge considerably from their Cp´2M

counterparts. For example, in contrast to the orange, air-stable ferrocene,

bis(indenyl)iron is a black solid and highly air-sensitive. Bis(indenyl)chromium is a

diamagnetic metal-metal bonded dimer {(C9H7)2Cr}2,134 unlike the monomeric,

paramagnetic Cp2Cr.136 Until recently, when M = Mn, a comparison between

cyclopentadienyl and indenyl-based species could not even made, as neither

bis(indenyl)manganese, nor any substituted derivative of it, had been reported.137-139

This was a curious omission, given that cyclopentadienyl complexes of MnII in

the form of the well-studied manganocenes have been known for over 50 years.60,140-142

66

As mentioned in previous chapters, manganocenes are unique among first-row

metallocenes for having two energetically accessible spin states that can be readily

interconverted based on the substituents of the cyclopentadienyl ligands. In the absence

of extreme steric congestion,141,143 electron-donating substituents on the rings (e.g.,

alkyls) support a low-spin (2E2g) configuration, whereas less electropositive groups (e.g.,

H, SiMe3) favor a high-spin (6A1g) state. Manganocenes have been used as one-electron

donors in magnetically ordered charge-transfer salt complexes,144-146 and given that

bis(indenyl) complexes of iron have been explored as effective alternatives to

metallocene donors in such compounds,147 (Ind)´2Mn(II) species would also be of

interest.

We describe here methylated bis(indenyl) complexes of MnII, some of which were

mentioned at the end of Chapter II. These new compounds focus on methylated indenyl

ligands, and display substantial differences from structures seen previously for

manganocenes owing to the greater bonding flexibility of the indenyl ligand.

Experimental

General Considerations. All manipulations were performed with the rigorous

exclusion of air and moisture using Schlenk or glovebox techniques. Proton (1H) NMR

experiments were obtained on a Bruker DPX-300 spectrometer at 300 MHz, Bruker

DPX-400 at 400 MHz or Bruker DRX-501 spectrometer at 500 MHz. Elemental analyses

were performed by Desert Analytics (Tucson, AZ). Melting points were determined on a

Laboratory Devices Mel-Temp apparatus in sealed capillaries. Mass spectra were

obtained using a Hewlett-Packard 5890 Series II gas chromatograph/mass spectrometer.

67

Materials. Anhydrous manganese(II) chloride (99.999%) was purchased from

Alfa Aesar and used as received. Indene, 2-methylindene, methacryloyl chloride, p-

xylene, 3-chloropropionyl chloride, n-butyl lithium, potassium bis(trimethylsilyl)amide,

p-toluenesulfonic acid, anhydrous pentane, and anhydrous, unstabilized tetrahydrofuran

(THF) were purchased from Aldrich and used as received. Hexanes, toluene, and diethyl

ether were distilled under nitrogen from potassium benzophenone ketyl. Toluene-d8

(Aldrich) was vacuum distilled from Na/K (22/78) alloy and stored over type 4A

molecular sieves prior to use.

Magnetic Measurements. Solution magnetic susceptibility measurements were

performed on a Bruker DRX-400 spectrometer using the Evans’ NMR method.148 The

paramagnetic material (5–10 mg) was dissolved in toluene-d8 in a 1.0 mL volumetric

flask. The solution was thoroughly mixed, and approximately 0.5 mL was placed in an

NMR tube containing a toluene-d8 capillary. The calculations required to determine the

number of unpaired electrons based on the data collected have been described

elsewhere.149

General Procedures for X-ray Crystallography. A suitable crystal of each

sample was located, attached to a glass fiber, and mounted on a Bruker SMART APEX II

CCD Platform diffractometer for data collection at 173(2) K or 100(2) K. Data collection

and structure solutions for all molecules were conducted at the X-ray Crystallography

Facility at the University of Rochester by Dr. William W. Brennessel or at the

University of California, San Diego by Dr. Arnold L. Rheingold. Data resolution of

0.84 Å were considered in the data reduction (SAINT 7.53A, Bruker Analytical Systems,

Madison, WI).

68

The intensity data were corrected for absorption and decay (SADABS). All

calculations were performed using the current SHELXTL suite of programs.150 Final cell

constants were calculated from a set of strong reflections measured during the actual data

collection.

The space groups were determined based on systematic absences (where

applicable) and intensity statistics. A direct-methods solution was calculated that

provided most of the non-hydrogen atoms from the E-map. Several full-matrix least

squares/difference Fourier cycles were performed that located the remainder of the non-

hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement

parameters. All hydrogen atoms were placed in ideal positions and refined as riding

atoms with relative isotropic displacement parameters.

Synthesis of 2,4,7-trimethylindene, HInd3Me-2,4,7. AlCl3 (62.82 g, 0.47 mol) was

slurried in 250 mL of CS2 in a 500 mL Schlenk flask that had been flushed with N2.

Methacryloyl chloride (49.25 g, 0.47 mol) and p-xylene (50.07 g, 0.47 mol) were added

to an addition funnel along with ~20 mL of CS2 and the funnel was attached to the

Schlenk flask. The methacryloyl chloride and p-xylene were added dropwise at 0 ºC

under nitrogen, gradually turning the solution dark red. The reaction was stirred

overnight while gradually warming to room temperature. The solution was refluxed the

following day for 4 h at 55-60 ºC. The solution was cooled to room temperature and

poured slowly over ~500 g of ice that had been slurried with concentrated HCl (200 mL),

turning the solution yellow. The solution was allowed to stir until it had warmed to room

temperature, then the organic layer was separated and neutralized with aqueous NaHCO3.

The remaining organic solution was dried with MgSO4 and the solvent removed by rotary

69

evaporation to yield 69.47 g of an orange-red oil. The oil was distilled at 70 ºC and 200

mTorr for 4 h to produce 13.03 g (16%) of the pale yellow indenone oil that was

characterized by GC/MS (m/e = 174).

The indenone was dissolved in anhydrous diethyl ether (75 mL) and chilled to 0

ºC in a 250 mL Schlenk flask before adding lithium aluminum hydride (44 mL of 1.0 M

diethyl ether solution, 0.044 mol) dropwise through a syringe. The reaction was stirred

overnight under nitrogen before refluxing at 65 ºC for 4 h. The solution was cooled to

room temperature before being neutralized by the slow addition of cold water (~4 mL),

aqueous NaHCO3 (~8 mL), and more cold water (~30 mL). The white precipitate that

formed was filtered off and the remaining solution neutralized with dilute NaHCO3. The

organic solution was dried with MgSO4 and the solvent removed by rotary evaporation to

leave the indenol product as a white crystalline solid (11.85 g, 90%). MS: m/e = 176.

The 2,4,7-trimethylindenol (11.85 g, 67 mmol) was dissolved in toluene (150 mL)

and added to a 250 mL round-bottom flask. A few crystals of p-toluenesulfonic acid were

added to a solution and the flask was fitted with a Dean-Stark trap and condenser. The

solution was refluxed until 1.2 mL of water was collected. The remaining golden colored

solution was neutralized with aqueous NaHCO3 and water before drying with MgSO4 and

removing the solvent by rotary evaporation. The remaining orange oil was then added to

a sublimation apparatus where the indene was obtained as a white crystalline solid (7.30

g, 69%) by fractional sublimation at 60 ºC and 300 mTorr over 3 hours. MS: m/e = 158.

1H NMR (500 MHz, ppm in CDCl3): δ 6.9 (doublet, 1 H), 6.8 (doublet, 1 H), 6.5

(singlet, 1 H), 3.2 (singlet, 2 H), 2.4 (singlet, 3H), 2.3 (singlet, 3H), 2.2 (singlet, 3H).

70

Synthesis of Potassium 2,4,7-trimethylindenide, K[Ind3Me-2,4,7]. 2,4,7-

trimethylindene (2.96 g, 18.7 mmol) was dissolved in toluene (40 mL) in a 250 mL

Erlenmeyer flask. Potassium bis(trimethylsilyl)amide, K[N(SiMe3)2] (3.55 g, 17.8

mmol), was dissolved in toluene (30 mL) and added dropwise to the indene solution

while stirring. The solution immediately turned pale yellow upon the onset of addition,

but after stirring for 24 h at room temperature, the solution became yellow-green.

Hexanes were added (175 mL) to fully precipitate the potassium indenide salt, which was

then filtered over a medium-porosity frit, washed with hexanes (2 x 25 mL), and dried

under vacuum to yield 2.60 g (74%) of a blue-gray powder that was confirmed to be the

indenide salt by 1H NMR (300 MHz) in toluene-d8: δ 2.24(singlet, 3H, CH3 in the 2-

position); 2.34 (singlet, 6H, CH3 in the 4,7-positions); 6.56 (multiplet, 3H, CH in the

1,2,3-positions); 7.20 (doublet, 2H, CH in the 5,6-positions).

Synthesis of 4,7-dimethylindene, HInd2Me-4,7. 200 mL of CS2 was added to a 500

mL Schlenk flask containing AlCl3 (31.51 g, 0.2363 mol) and cooled to 0 °C in an ice

bath. A solution containing p-xylene (25.01 g, 0.2356 mol) and 3-chloropropionyl

chloride (29.896 g, 0.2355 mol) was added dropwise through an addition funnel, and the

resulting reaction solution allowed to warm to room temperature. The solution was then

refluxed at 55 °C for 2.5 h with a drying tube attached. After cooling to room

temperature, the now red solution was poured over ~500 g of ice and stirred until the

whole solution turned light yellow. The organic layer was neutralized with NaHCO3 and

dried with MgSO4 before removing the remaining CS2 by rotary evaporation. The

remaining orange-yellow oil (~45 mL) was added dropwise to excess H2SO4 at 0 °C,

turning the solution dark red. The solution was then warmed to room temperature before

71

refluxing at 80 °C for 1 hour, at which point the evolution of HCl gas had stopped. The

solution was poured over ice and the slurry was allowed to stir while warming to room

temperature, resulting in an orange solution. The product was extracted with diethyl ether

and the solution was neutralized with NaHCO3 before being dried with MgSO4. Removal

of the solvent by rotary evaporation yielded a mixture of white and yellow crystals that

was purified by redissolving the product in warm methanol and placing in a freezer

overnight at -20 °C. The resulting white crystals of 4,7-dimethy-1-indanone were isolated

by filtration to yield 23.48 g (62%) of product whose identity was confirmed by GC/MS

(m/e = 160).

The indanone (23.48 g, 0.1468 mol) was dissolved in anhydrous diethyl ether

(250 mL) under nitrogen and chilled to 0 °C in a 500 mL Schlenk flask. 50 mL of 2.0 M

Li[AlH4] in diethyl ether was added dropwise through an addition funnel and the

resulting solution stirred overnight at room temperature. The solution was refluxed at 55-

60 °C the following day for 5 h. The mixture was then cooled to 0 °C and quenched by

adding 3 mL of cold water, 5 mL of dilute NaOH and another 15 mL of cold water. The

white precipitate that formed was filtered and the remaining organic solution was dried

with MgSO4. Removal of the solvent by rotary evaporation yielded 14.10 g (59%) of

white, crystalline 4,7-dimethyl-1-indanol, confirmed by GC/MS (m/e = 162).

The indanol was dissolved in 150 mL of toluene and added to a 250 mL round-

bottom flask with a Dean-Stark trap and condenser attached. A few crystals of p-

toluenesulfonic acid were added to the solution and the solution was refluxed for 2.5 h

until approximately 1.5 mL of water had been collected in the trap. The solution was then

cooled to room temperature and neutralized with NaHCO3 before being dried with

72

MgSO4. Rotary evaporation to remove the remaining toluene gave 11.93 g (95%) of a

yellow oil that was then distilled at 35 °C and 50 mTorr to yield 8.22 g of a clear liquid

that was confirmed to be 4,7-dimethylindene by GC/MS (m/e = 144) and 1H NMR: δ 2.3

(s, 3H), 2.4 (s, 3H), 3.2 (t, 2H), 6.5 (dt, 1H), 6.8-7.2 (m, 3H).

Synthesis of Potassium 4,7-dimethylindenide, K[Ind2Me-4,7]. 4,7-

Dimethylindene (3.724 g, 25.9 mmol) was dissolved in toluene (50 mL) in a 250 mL

Erlenmeyer flask. Potassium bis(trimethylsilyl)amide, K[N(SiMe3)2] (4.300 g, 21.6

mmol), was dissolved in toluene (30 mL) and added dropwise to the indene solution

while stirring. The solution immediately turned yellow upon the onset of addition, but

after stirring for 24 h at room temperature, the solution became an opaque gray color.

Hexanes (125 mL) were added to fully precipitate the potassium indenide salt, which was

then filtered over a medium-porosity frit, where it was washed with hexanes (2 x 20 mL)

and dried under vacuum to yield 3.794 g (95%) of a gray powder. The powder was

confirmed to be the indenide salt by 1H NMR (300 MHz) in toluene-d8: δ 2.34 (singlet,

6H, CH3 in the 4,7-positions); 6.56 (multiplet, 3H, CH in the 1,2,3-positions); 7.20

(doublet, 2H, CH in the 5,6-positions).

Synthesis of Bis(2,4,7-trimethylindenyl)manganese(II), (Ind3Me-2,4,7)2Mn.

MnCl2 (0.126 g, 1.00 mmol) and a stir bar were added to a 125 mL Erlenmeyer flask.

THF (50 mL) was added to the flask and the MnCl2 was dispersed by stirring for 1 h.

Potassium 2,4,7-trimethylindenide, K[Ind3Me-2,4,7], (0.404 g, 2.06 mmol) was dissolved in

30 mL of THF and added to a 60 mL addition funnel. The K[Ind3Me-2,4,7] was added

dropwise over 30 min into the flask containing MnCl2 and allowed to stir overnight;

removal of the solvent by vacuum left behind an orange oil. The product was then

73

extracted with pentane (5 x 30 mL) and filtered to remove the KCl precipitate. The

orange pentane filtrates were combined and most of the solvent was then removed under

vacuum. The remaining solvent was then allowed to evaporate at room temperature over

2 days, affording a dark orange solid, mp 146–150 °C (0.252 g, 67%). Crystals suitable

for crystal structure determination were eventually obtained from a sealed solution of

[(Ind3Me-2,4,7)MnCl(thf)]2 dissolved in toluene that remained at room temperature for 10

days. Anal. Calcd. for C24H26Mn: C, 78.03; H, 7.09; Mn, 14.87. Found: C, 78.64; H,

7.31; Mn, 14.9. Solution magnetic susceptibility (µeff298K): 5.68 µB.

Synthesis of Bis(4,7-dimethylindenyl)manganese(II), (Ind2Me-4,7)2Mn. MnCl2

(0.344 g, 2.73 mmol) was added to a 125 mL Erlenmeyer flask fitted with a stir bar and

30 mL of THF. The flask was stirred at room temperature for 1 h to disperse the MnCl2.

Potassium 4,7-dimethylindenide (1.001 g, 5.11 mmol) was dissolved in THF (20 mL) and

added dropwise to the flask containing MnCl2. The reaction was allowed to stir

overnight at room temperature before the removal of the solvent under vacuum left an

orange residue. Three extractions with pentane (20 mL each) were performed yielding a

lightly colored solution; only an orange oil remained when the solvent was removed. The

remaining orange product that was not extracted into pentane was then extracted with 40

mL of toluene, and 30 mL of this solution was placed in the freezer at –20 °C for 3 days.

Dark orange crystalline blocks grew from the solution (58 mg, 26% yield), mp 260-265

°C. Anal. Calcd. for C22H22Mn: C, 77.41; H, 6.50. Found: C, 78.86; H, 6.72. Solution

magnetic susceptibility was not obtained owing to the lack of solubility in toluene once

the crystals had formed.

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Synthesis of Potassium Tris(4,7-dimethylindenyl)manganate-(II),

[K(dioxane)1.5][Mn(Ind2Me-4,7)3]. MnCl2 (0.217 g, 1.72 mmol) was added to a 125 mL

Erlenmeyer flask fitted with a magnetic stirring bar and 30 mL of THF. The flask fitted

with a magnetic stirring bar and 30 mL of THF. The flask was stirred at room

temperature for 1 to disperse the MnCl2. Potassium 4,7-dimethylindenide (0.917 g, 5.03

mmol) was dissolved in THF (20 mL) and added dropwise to the flask containing MnCl2.

The reaction mixture was stirred overnight at room temperature; removal of the solvent

under vacuum left a red solid. The residue was then extracted with 1,4-dioxane (2 x 30

mL), and the solvent was removed under vacuum to yield 0.323 g (29%) of a red powder.

Crystals were grown by dissolving the product in a 1,4-dioxane/toluene mixture (3:1) and

allowing the solvent to evaporate slowly at room temperature, mp 308-312 °C (dec).

Anal. Calcd for C39H45KMnO3: K, 5.96; Mn, 8.38. Found: K, 5.15, Mn 8.07.

Attempted synthesis of Bis(2-methylindenyl)manganese(II), (IndMe-2)2Mn.

MnCl2 (0.388 g, 3.08 mmol) was added to a 250 mL Erlenmeyer flask fitted with a stir

bar. THF (20 mL) was added and the flask was stirred at room temperature for 1 h to

disperse the MnCl2. Potassium 2-methylindenide (1.014 g, 6.04 mmol) was dissolved in

THF (25 mL) at room temperature and added dropwise into the flask containing MnCl2,

yielding an orange solution. The solution was allowed to stir overnight at room

temperature before the solvent was removed under vacuum, leaving a light yellow solid.

Pentane (20 mL) was added to the flask and the liquid was decanted into a medium

porosity glass frit, but the solution came through colorless, indicating that no product had

been extracted. Toluene (3 × 20 mL) was used instead to extract the expected

bis(indenyl) product and the extract filtered over a medium porosity frit. The orange

75

toluene filtrate was collected and used in an attempt to grow crystals by various methods,

including slow cooling in a toluene solution, slow removal of solvent under vacuum, and

diffusion of aliphatic solvents. Unfortunately, only an orange oil was ever isolated. There

were a few crystals that grew above the oil when hexanes were allowed to evaporate at

room temperature; however, there were only enough to acquire a crystal structure, and

these crystals were not of the expected bis(2-methylindenyl)manganese(II) compound.

Instead the crystal structure proved to be of the aryloxide containing complex (IndMe-

2)3Mn2(BHT). Butylatedhydroxytoluene (BHT) is used in trace amounts in THF as an

inhibitor, but in this case reacted with the Mn center(s). Further attempts to use BHT-free

THF in order to obtain the desired bis(indenyl) complex have been unsuccessful.

Attempts to remake (IndMe-2)3Mn2(BHT) are described in detail in Chapter V.

Results

Ligand Synthesis. An extensive library of substituted indenes is available either

by direct reaction with indenide salts,151,152 or by Friedel-Crafts-assisted ring assembly

from substituted benzenes.153 The indenes used in this study were readily deprotonated

by n-BuLi or K[N(SiMe3)2] in hexanes or toluene, and the resulting air-sensitive salts

were isolated in moderate to high yield.

Ligand and Metal Complex Synthesis. Bis(indenyl)manganese(II) complexes

were synthesized by salt metathesis elimination reactions of the appropriate indenide salts

with MnCl2 in THF (eq 1).

2 M[Ind´] + MnCl2 Ind´2Mn + 2 MCl↓ (M = Li or K) (1)

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After the removal of THF under vacuum, addition of pentane or toluene served to

extract the manganese complexes, allowing for the removal of the alkali metal chloride

by-products. The purified (indenyl)manganese complexes were crystallized either by

slow evaporation of a saturated solution, or by cooling of a concentrated solution to

approximately -30 °C. They vary in color from bright orange to dark red-orange, and all

are highly air- and moisture-sensitive.

It should be noted that the preparation of the indenyl complexes requires

chemicals and reagents of very high quality in order to achieve consistent results. In

particular, the purity of the manganese chloride has proven critical; initial experiments

with commercially available anhydrous MnCl2 (specified with 97% purity, and

satisfactory for the preparation of manganocenes25) led to the formation of intractable

red-orange oils that decomposed to brown materials over the course of several days. The

use of MnCl2 beads of >99.99% purity led to consistently reproducible reactions and to

compounds that are indefinitely stable under an inert atmosphere.

Butylhydroxytoluene (BHT) is a stabilizer used in small quantities (0.025%) in

anhydrous THF. In cases where large volumes of THF are used, the butylhydroxytoluene

anion is likely formed from the deprotonation of BHT with various potassium indenide

ligands. This can be a problem as the BHT anion can react and coordinate to MnII

centers. This was seen when a product containing a bridging BHT as an aryloxide was

isolated while trying to synthesize (IndMe-2)2Mn. This result generated interest in

intentionally synthesizing additional MnII aryloxide compounds. These compounds were

subsequently explored and are discussed in Chapter V.

77

Manganese complexes of the [4,7-Me2C9H5]– anion were obtained in two forms;

crystals of the toluene-solvated (4,7-Me2C9H5)2Mn were only marginally acceptable for

single-crystal X-ray study, but proved to form a cyclic octomer (see below). As the

bis(indenyl) compound accounted for only 26% of the theoretical reaction yield, a

separate extraction was performed using 1,4-dioxane to obtain additional manganese-

containing product. After the extraction, the [K(dioxane)1.5][(Mn(Ind2Me-4,7)3] salt was

isolated; its formation likely occurred due to the reaction of previously unreacted

potassium indenide salt with (4,7-Me2C9H5)2Mn. This compound can be prepared in

moderate to good yield by allowing 3 equivalents of the potassium indenide salt to react

with 1 equivalent of MnCl2. This reaction is represented by eq 2.

3 K[Ind2Me-4,7] + MnCl2 [K(dioxane)1.5][(Mn(Ind2Me-4,7)3] + 2 KCl↓ (2)

Except for the poorly soluble (Ind2Me-4,7)2Mn, the solution magnetic

susceptibilities of the other crystalline compounds were measured with Evans’ method.148

In all cases, a room temperature value consistent with high spin Mn(II) (cf. 5.92 µB for

the spin-only value for S = 5/2) was obtained.

Crystallographic Results

{(Ind2Me-4,7)2Mn}8. Crystals of (Ind2Me-4,7)2Mn were isolated from a toluene

solution as dark orange blocks. The presence of multiple, extensively disordered solvent

molecules in the unit cell lowered the resolution of the structure, so that bond lengths and

angles cannot be discussed in detail.154 Repeated attempts to grow more satisfactory

crystals were not successful.

dioxane

78

The structure is constructed of an octameric ring of manganese atoms with a

crystallographically imposed 2-fold axis (Figure 53). The ring is puckered, with the

metal atoms separated by distances of 5.1–5.2 Å; they alternate above and below the

mean M8 plane by maximum distances of 1.2 and 1.1 Å. Each manganese center is

associated with three 4,7-dimethylindenyl ligands. One of these ligands is terminal, and

although appearing somewhat slipped, is approximately η5-bound to the manganese

centers. The bridging ligands display η1-coordination to the manganese atoms at an

average distance of 2.3 Å, and alternate their positions above and below the Mn8 ring.

Figure 53. Plot of the non-hydrogen atoms of {(Ind2Me-4,7)2Mn}8.

79

[K(dioxane)1.5][(Mn(Ind2Me-4,7)3]. Extraction of the residue of the reaction to

form (Ind2Me-4,7)2Mn with 1,4-dioxane produced a solution that deposited yellow

hexagonal plates. An ORTEP of the molecule is shown in Figure 54, which gives the

numbering scheme that is referred to in the text. Figure 55 shows a projection of the

three-dimensional structure and Table 2 gives selected bond lengths.

There are six crystallographically independent manganese atoms in the

asymmetric unit, although all six have very similar carbon bonding distances and

arrangements of the indenyl ligands. The general coordination geometry around each

manganese atom is a paddlewheel of three η2-bound 4,7-dimethylindenyl ligands. The

average Mn–C contacts are at 2.337(5) and 2.404(5) Å for C1 and C2, respectively, and

the other Mn…C contacts are >2.75 Å, and are considered to be nonbonding. The

indenyl ligands are involved in cation–π bonding to the potassium through either the 5-

membered rings in one half of the molecules (K–C distances range from 3.00 Å to 3.24

Å), or the 6-membered rings in the other half (K–C distances range from 3.00 Å to 3.47

Å). Every potassium cation is coordinated by a 6-membered ring, a 5-membered ring,

and one oxygen atom on each of two dioxane molecules. This coordination extends in

two-dimensions, forming a layer of cations and anions. One of the two dioxane

molecules bound to the potassium cation is bridging to a separate potassium cation of

another layer, essentially creating a bilayer system held together with the bridging

dioxane molecules, with no interactions between separate bilayers.

The η2-coordination is established from the range of manganese bond distances to

C(1) and C(2) (Mn–C(1) = 2.29 Å to 2.34 Å, Mn–C(2) = 2.37 Å to 2.42 Å) which are

significantly shorter than the distances to C(3) and C(8) (Mn–C(3) = 2.86 Å to 2.91 Å,

80

Mn–C(8) = 2.78 Å to 2.84 Å). There are few other compounds known to exhibit η2-

coordination of a Cp to a manganese center,155 yet one of these is the manganocene

polymer. Those distances for η2-coordination (2.44 Å and 2.62 Å) are much longer than

the distances reported here. The structure of [K(dioxane)1.5][(Mn(Ind2Me-4,7)3] is very

similar to that of [(η2-Cp)3MnK(thf)1.5],155 in which the three Cp ligands are arranged in a

paddlewheel around each Mn center, and each Cp is cation-π bound to a potassium

counter ion. With THF as the solvent molecule, the structure forms a single layer with

ca. 9.5 Å between sheets. As a comparison, a single sheet of the bilayer in the indenyl

complex is ca. 8.1 Å, and the distance between bilayers is 16.0 Å, making the crystals

fragile in two dimensions.

Table 2. Select bond distances and averages for [K(dioxane)1.5][(Mn(Ind2Me-4,7)3].

Atoms Distance (Å) Atoms Distance (Å)

Mn(1)–C(1) 2.337(4) Mn(1)–C(2) 2.405

Mn(2)–C(1) 2.330(5) Mn(2)–C(2) 2.375

Mn(3)−C(1) 2.332(5) Mn(3)−C(2) 2.419

Mn(4)−C(1) 2.298(5) Mn(4)−C(2) 2.397

Mn(5)−C(1) 2.311(5) Mn(5)−C(2) 2.418

Mn(6)−C(1) 2.285(5) Mn(6)−C(2) 2.413

Avg. Mn–C(1) 2.32(1) Avg. Mn–C(2) 2.40(1)

Avg. K−C(η5) 3.09(1) Mn(1)−C(3),C(4),C(5) Mn(2)−C(3),C(4),C(5)

> 2.72

Avg. K−C(η6) 3.27(1)

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Figure 54. ORTEP of the non-hydrogen atoms of [K(dioxane)1.5][(Mn(Ind2Me-4,7)3], illustrating the numbering scheme used in the text. Thermal ellipsoids are shown at the 50% level.

Figure 55. Projections down the crystallographic c (left) and a (right) axes of [K(dioxane)1.5][(Mn(Ind2Me-4,7)3]; manganese atoms are in orange; potassium in purple. The c projection shows only one-half a bilayer; the a projection shows the two adjacent bilayers

(Ind3Me-2,4,7)2Mn. Orange needles were extracted from a solution of [(Ind3Me-

2,4,7)MnCl(thf)]2 in pentane. An ORTEP of an expanded asymmetric unit for the

82

polymeric molecule is shown in Figure 56, which gives the numbering scheme that is

referred to in the text. Selected bond lengths and angles are shown in Table 3.

The asymmetric unit contains one manganese atom and two indenyl ligands, one

that is η1 and one that is η5 bound. Each manganese atom is also coordinated to a third

indenyl ligand that is symmetry equivalent to the η1 bound species, creating an overall

structure that is polymeric in one dimension. The general coordination geometry around

each manganese is very similar to that seen in {(Ind2Me-4,7)2Mn}8. The ligand hapticities

can be identified in this complex from their bond distances. For the η1 bound indenyl, the

Mn-C bond is 2.323(3) Å for C13 and C15a. The bond lengths to the other carbons on

each ligand are all >2.8 Å. The η5 bound ring is significantly slipped, as the ΔMn-C value

of 0.32 Å is large enough to potentially be considered η3 bound; however, the average

Mn-C distance of 2.459(7) is still within the range of what is considered to be η5 bound.

Additionally, since {(Ind3Me-2,4,7)2Mn}n is polymeric, there is steric crowding from the

indenyl ligands, with C…C contacts approaching 3.5 Å between the benzo methyl groups

(C24) of the bridging indenyl ligands to the benzo carbons (C6 and C7) of the terminal η5

bound ligand. Ligand contortions on a monomeric species would likely be far less given

the relatively small size of the methyl group ligand substituents.

83

Table 3. Selected bond distances of (Ind3Me-2,4,7)2Mn.


Mn(1)–C(1) 2.522(3) C(1)–C(2) 1.406

Mn(1)–C(2) 2.377(3) C(2)–C(3) 1.423

Mn(1)−C(3) 2.300(3) C(3)−C(9) 1.437

Mn(1)−C(9) 2.475(3) C(9)−C(8) 1.442

Mn(1)−C(8) 2.620(3) C(8)−C(1) 1.429

Avg. Mn–C(1) 2.456(7)

Mn(1)−C(13) 2.291(3) ΔMn−C =0.32

Figure 56. Polymeric structure of (Ind3Me-2,4,7)2Mn.

84

Figure 57. Asymmetric unit of (Ind3Me-2,4,7)2Mn.

Discussion

In contrast to the low-spin or spin crossover behavior observed in methyl

substituted cyclopentadienyl compounds,27,156,157 bis(indenyl)manganese(II) complexes

have all been found to be high spin. This is confirmed both by magnetic susceptibility

measurements (spin-only value of S = 5/2 is 5.92 µB) as well as the length of Mn−C

bonds in the crystal structures. High spin Cp’2Mn complexes have an average Mn−C

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bond distance near 2.4 Å, whereas the average is around 2.1 Å for low spin complexes.27

The average length of the Mn−C bond is over 2.4 Å for all bis(indenyl) complexes. These

distances alone are suggestive of a high spin Mn(II) center, the assignment of which has

been supported by all available magnetic data.

The high spin nature of the bis(indenyl)manganese(II) complexes is also different

from similar complexes of CrII, in which the complexes with Ind2Me-4,7 or Ind3Me-2,4,7

showed spin crossover behavior.35,36 This difference can be explained by the fact MnII

has 5 unpaired d- electrons, which require more spin-pairing energy to leave only 1

electron in the low-spin state than do the 4 d electrons of CrII, whose conformation

changes from 4 to 2 unpaired electrons. Also, some of the structures are quite different;

(Ind2Me-4,7 )2Mn is an octomer in the solid state, for example, as opposed to the

monomeric sandwich structure of its chromium counterparts, which also influences the

spin state of the molecule.

An increase in the donor character of the Cp ligand is afforded by the addition of

alkyl donating groups, such as those in 1,1′-dimethylmanganocene.25 This simple

modification from the parent Cp2Mn is enough to lower the HOMO–LUMO gap to an

energy that supports a spin-crossover state. As an adjunct to this work, methylation of

the C5 ring on the indenyl ligand and the subsequent incorporation of the modified

ligands into MnII complexes was pursued. The tendency of these compounds to form

orange to red oils that show signs of decomposition after a day initially hindered

characterization. However, more recently it has been discovered that the use of higher

purity MnCl2sources, solvents without added stabilizers, and less than two full

86

equivalents of the methylated indenide per manganese atom, produces complexes that do

not decompose upon standing.

Given the need for a stronger donating ligand, a more heavily methylated indene,

2,4,7-trimethylindene, was synthesized and deprotonated. The reaction of two

equivalents of the ligand with one equivalent of MnCl2 produced bright-orange, highly

branched crystals that were unsuitable for x-ray crystallography. Crystals of this

compound were eventually obtained from a solution of the mono(indenyl)manganese(II)

halide that underwent Schlenk-type equilibrium to produce the bis(indenyl)manganese

complex (a process explained and discussed in Chapter IV). Elemental analysis of C, H,

and Mn confirmed the composition of (Ind3Me-2,4,7)2Mn, and this compound was

established to be high-spin by solution magnetic susceptibility methods (5.68 µB). This

result would suggest the need for even stronger donor substituents such as isopropyl or t-

butyl groups to promote a spin-crossover or low-spin complex; however, there is

evidence t-butyl groups can paradoxically support a high-spin state due to their steric

bulk,33 and there has been a report of the high-spin complex bis(1,3-

diisopropylindenyl)manganese(II).158

Conclusions

We have synthesized the first indenyl manganese(II) systems. As anticipated

from manganocene and its derivatives, bis(indenyl)manganese(II) complexes display a

wide range of Mn–C bond distances, as well as various hapticities of the indenyl ligand.

This makes direct comparisons of the reactivity among the metal centers difficult due to

their different coordination environments.

87

Indenyl ligands with only methyl substituents do not provide enough steric

hindrance to prevent access to the manganese center. The divergence from the typical

sandwich compounds observed in transition metal complexes is unexpected, although not

unreasonable due to the larger metal radius and the fact that in high-spin d5 complexes

there is no ligand field stabilization energy. Manganese centers bound to two or more

indenyl ligands favor the high-spin state regardless of the coordination environment, as

seen from the magnetic properties of the trimethylsilylated, isopropylated, and

methylated species. In the cases of methyl substitution on the indenyl ring, the ease of

ring slippage combined with the lack of steric bulk allows for more than two ligands

(indenyl, solvent, or otherwise) to bind the metal center. The generation of low-spin or

spin-crossover complexes may be more likely with the use of more heavily methylated

ligands. Alternative substituents which have been investigated include ethyl and

isopropyl groups.158 Bulkier groups, such as t-butyl or trimethylsilyl, may be less capable

of supporting the shorter Mn–C bond distances of the low-spin state due to the steric

repulsion of the opposing ring. In comparison, shorter metal–carbon bond distances do

appear in the complexes (Ind2Si-1,3)2M (M = V, Cr,33 or Fe159), giving further evidence

that manganese requires a higher ligand field strength to produce low-spin complexes

than do other first row metals.

88

CHAPTER IV

SYNTHESES, STRUCTURES, AND REACTIVITIES OF MONO(INDENYL)MANGANESE(II) HALIDES

Introduction

Along with the synthesis of the new methylated bis(indenyl) complexes of MnII

discussed in Chapter III, a series of dimeric indenyl manganese(II) halides (halide =

chloride or iodide) have also been synthesized. Unlike what has been found for some of

the bis(indenyl) complexes, the dimeric mono(indenyl)manganese halides show

remarkable structural similarity to their Cp analogs.98 Figure 39 in Chapter II shows an

example of one of these Cp compounds, which features CpMe-1, bridging chlorides, and

triethylphosphine ligands. Both the Cp and indenyl complexes feature the same dimeric

bridging halide structure, as well as being high spin with antiferromagnetically coupled

Mn centers.

The indenyl and Cp manganese halides are also both observed to exhibit Schlenk

equilibrium in solution. Schlenk equilibrium is a phenomenon most often associated with

magnesium and other group II metals, and in particular, Grignard reagents.160 Grignard

reagents are alkylmagnesium halides (MgRX), which in solution undergo constant

rearrangement to form the magnesium halide and dialkyl magnesium compounds as

shown below.160 While this behavior is not often seen with manganese compounds,

high-spin MnII does share similarities with MgII, so this parallel reactivity should not be

completely unexpected. The two metals are very similar in size, as mentioned in Chapter

II (rMnII = 0.81 Å; rMgII = 0.86 Å)50,51. In addition, high-spin MnII lacks any ligand field

89

stabilization energy due to its 5 unpaired electrons. This is part of the reason MnII will

display very ionic behavior in some of its compounds, a feature that is much more similar

to magnesium than is the case other transition metals.

2 MgRX MnR2 + MnX2 (3)

This series of indenyl compounds is unique, however, due to the reactivity

observed with molecular oxygen while in solution, a feature not shared with the Cp

analogs. At low temperature (-78 °C) and very low concentrations of oxygen (single ppm

level), several [MnIndX(thf)]2 compounds undergo a dramatic color change from yellow-

orange to dark blue. This has been attributed to the coordination of the trace amounts of

oxygen to form a superoxoide or peroxide species.

Reactions of manganese with both molecular oxygen and superoxide have been of

interest for some time due to their relevance in manganese containing enzyme functions,

particularly manganese superoxide dismutase and catalase, as well as the oxygen-

evolving complex (OEC) in photosystem II.161-165 However, the exact mechanisms of

some of these processes are not fully understood, making reactions of manganese with

oxygen of particular interest for helping to design useful models of biological systems.

There are a few different forms oxygen can take when it coordinates to metal

centers: it can stay a neutral ligand and coordinate as dioxygen, it can be reduced once to

O2- and become superoxide, or it can be reduced twice to O2

2- and become peroxide. The

identity of these species is usually identifiable through various methods of spectroscopy,

which will be described below.

There have been a small number of dioxygen, superoxide- and peroxide

complexes of manganese documented,166-170 but few have actually been derived by

90

reaction with molecular oxygen.171,172 Instead, nearly all are formed by either a direct

reaction with a superoxide source, or more commonly, by reaction with hydrogen

peroxide. The other Mn complexes capable of binding molecular oxygen are not air-

sensitive, and are able to be pressurized with oxygen to help facilitate coordination. The

fact that the organometallic compounds discussed in this chapter are highly air-sensitive,

and cannot simply be pressurized with oxygen, makes isolation of the oxygenated species

difficult and full quantification of the reactivity almost impossible. The sensitivity of

these compounds, down to low (< 5ppm) levels of O2, is a major source of the interest in

their behavior. While the effective limit of detection of oxygen for these compounds is

extremely low, the upper window of oxygen concentration needed to decompose the

compounds is almost equally as low, causing challenges throughout the characterization

process.

Characterization of dioxygen adducts of manganese and peroxo- and

superoxomanganese compounds is typically done with a combination of methods

including UV-vis, infrared, Raman (and resonance Raman), and EPR (electron

paramagnetic resonance) spectroscopy, as well as mass spectrometry and X-ray

diffraction. For both peroxo and superoxo compounds of manganese, UV-vis serves as a

method to confirm the presence of the oxo species by the observation of two peaks in the

absorption spectrum: a narrower band in the range between 400-450 nm and a broader

band between 575-650 nm.170,171 While this technique is not effective in differentiating

between a superoxide and peroxide species, infrared spectroscopy and X-ray

crystallography (when applicable) can be used to do so. Superoxides will generally have

an O−O stretch in the range of 950-1200 cm-1 and will have O−O bond lengths in the

91

neighborhood of 1.20-1.35 Å.173 Peroxides, on the other hand, will usually have O−O

stretches in the range of 650-950 cm-1 and bond lengths around 1.38-1.55 Å.173 18O

labeling experiments are helpful for IR characterization because a clear shift can be seen

in the IR spectra for the O−O stretch. Isotopically labeled 18O experiments are also useful

with mass spectrometry to prove the presence of a coordinated O2 by observing a shift of

4 m/z units in the mass spectrum.171 The isotopically labeled experiments for IR and

mass spectrometry were not performed for the compounds in this study due to a lack of

18O availability.

Resonance Raman spectroscopy can also be used to identify the mode of oxygen

coordination and give insight into the M−O and O−O bonding in metal-O2 compounds.174

The last major characterization technique that can help to give insight onto the nature of

the metal-O2 bonding is electron paramagnetic resonance spectroscopy (EPR). This

technique can give information about the spin state, and consequently oxidation state, of

the metal center. For Mn (I = 5/2 for 55Mn), the hyperfine splitting can potentially

indicate whether a compound is MnII (A = 75-90 G) or MnIII (A = 50-65 G).175,176 These

trends hold true for monomeric species of coordination compounds that typically have

very defined (usually octahedral) geometries. Due to our complexes being

organometallic and also dimeric, at least in solution, the generic assignment of oxidation

state based on hyperfine splitting may not be applicable. However, an EPR spectrum

should still be able to indicate a change in the manganese environment, as well as the

presence of superoxide if it is formed.

We report here the preparation and characterization of a series of substituted

mono(indenyl)manganese(II) halides that display reactivity with molecular oxygen at low

92

concentrations to form what is tentatively assigned as a superoxide complex. Due to the

characterization challenges presented by the oxo-compounds, reactions with a number of

other potential oxidizing molecules were also examined.

Experimental









Alfa Aesar and used as received. Indene, 2-methylindene, methacryloyl chloride, p-

xylene, 3-chloropropionyl chloride, n-butyl lithium, potassium bis(trimethylsilyl)amide,

p-toluenesulfonic acid, anhydrous pentane, and anhydrous, unstabilized tetrahydrofuran

(THF) were purchased from Aldrich and used as received. Hexanes, toluene, and diethyl

ether were distilled under nitrogen from potassium benzophenone ketyl. Toluene-d8

(Aldrich) was vacuum distilled from Na/K (22/78) alloy and stored over type 4A

molecular sieves prior to use. Substituted indene ligands prepared as described in

Chapter III.



93





elsewhere.149

UV-Vis Spectroscopy. Electronic absorption spectra experiments were run in the

Que lab at the University of Minnesota. The experiments were run on a Hewlett-Packard

(Agilent) 8453 diode array spectrophotometer (190-1100 nm range) in quartz cuvettes

cooled using a liquid nitrogen cooled cryostat from Unisoku Scientific Instruments

(Osaka, Japan).

Electron Paramagnetic Resonance (EPR). X-band (9.62 GHz) EPR spectra

were recorded on a Bruker 300 spectrometer equipped with an Oxford ESR 910 cryostat

for low temperature measurements. The microwave frequency was calibrated with a

frequency counter and the magnetic field with an NMR gaussmeter. The temperature

was calibrated with a carbon-glass resistor temperature probe (CGR-1-1000, Lake Shore

Cryotronics).

Resonance Raman Spectroscopy. Resonance Raman spectra were collected on

an ACTON AM-506M3 monochromator with a Princeton LN/CCD data collection

system (LN-1100PB) using a Spectra Physics Model 2060 krypton laser or a Spectra

Physics Beamlok 2065-7S argon laser, and Kaiser Optical holographic super-notch

filters. Samples were frozen onto a gold-plated copper cold finger in thermal contact

with a Dewar flask containing liquid nitrogen. The Raman frequencies were referenced

to indene.

94

IR Spectroscopy. Solution IR spectra were recorded on a Thermo-Nicolet FT-IR

module instrument Magna 760 spectrometer at 4 cm-1 resolution. 10 mM samples in

toluene were run in an International Crystal Labs solution cell. Room temperature

samples were loaded in a glove bag under an argon atmosphere. For low temperature

experiments, the cell was brought into the glove box where it was cooled to -40 °C along

with the blue oxo-species. The sample was then loaded in the cell and immediately

transported out of the box and into the instrument while in a plastic bag to avoid water

condensation. The sample chamber of the instrument had been cooled with dry ice and

was purged with argon in attempt to keep the chamber both cold and dry.








Madison, WI).




collection.



95






Synthesis of {(2,4,7-trimethylindenyl)manganese(II)chloride(thf)}2, {(Ind3Me-

2,4,7)MnCl(thf)}2. MnCl2 (0.302 g, 2.40 mmol) was slurried in THF (50 mL) in a 250 mL

Erlenmeyer flask. After stirring for 45 min to disperse the MnCl2, K[Ind3Me-2,4,7] (0.475 g,

2.42 mmol) in THF (100 mL) was added dropwise to the MnCl2, gradually turning the

solution green-yellow. After stirring overnight, the THF was removed under vacuum,

leaving a yellow solid. The product was extracted with pentane (3 x 30 mL) and filtered

over a medium porosity frit to remove the KCl precipitate. During filtration, the filtrate

turned dark green when passing through the frit, and remained that color for about one

minute before returning to light yellow in color. The light yellow solution was then

evaporated to dryness, leaving 0.321 g (43%) of a yellow-orange solid. The remaining

product was redissolved in pentane, and was slowly cooled to -25 ºC to give green-yellow

needles that were of X-ray quality. mp 130-133 °C. Anal. Calcd. for C30H42O2Mn2Cl2:

C, 60.10; H, 6.62; Mn, 17.18. Found: C, 60.10; H, 6.84; Mn, 17.2. Solution magnetic

susceptibility: µeff (298 K): 7.27 µB.

Synthesis of {(2-methylindenyl)manganese(II)iodide(thf)}2, {(IndMe-

2)MnI(thf)}2. MnI2 (0.703 g, 2.28 mmol) dissolved in THF (50 mL) in a 250 mL

Erlenmeyer flask. After stirring for 1 h at room temperature to allow for dispersion of the

MnI2, a solution of potassium 2-methylindenide (0.383 g, 2.28 mmol) in THF (75 mL)

96

was added dropwise, resulting in an immediate change in color to golden yellow. After

stirring overnight, the THF was removed under vacuum, leaving an orange powder. An

attempted extraction with pentane did not remove any product. A second and third

extraction using toluene (20 mL) produced an orange solution, which turned green upon

passing through a medium porosity frit before changing back to orange upon standing.

The toluene extractions were then combined and the solution was concentrated by

removal of some of the solvent under vacuum. Hexanes were then added to the solution

to make approximately a 2:1 ratio of toluene to hexanes solution, and then slowly cooled

to – 10 °C for 3 days to produce 0.317 g (38%) of green crystalline blocks, mp 160-165

(dec). Anal. Calcd for C28H34O2Mn2I2: C, 43.87; H, 4.47; Mn, 14.35; I, 33.1. Found: C,

43.71; H, 4.54; Mn, 13.68; I, 34.4.

Attempted synthesis of {(2-methylindenyl)manganese(II)chloride(thf)}2,

{(IndMe-2)MnCl(thf)}2. MnCl2 (0.279 g, 2.22 mmol) was added to a 250 mL Erlenmeyer

flask and dispersed in THF (50 mL) by stirring at room temperature for 1 h. Potassium 2-

methylindenide (0.379 g, 2.25 mmol) was then dissolved in 75 mL of THF and added

dropwise through an addition funnel to the MnCl2 solution. The bright yellow solution

was allowed to stir overnight at room temperature, turning orange overnight. The solvent

was removed under vacuum to leave a yellow-orange residue. The product was extracted

first with pentane (3 x 30 mL), but it was not very soluble. The pale yellow solution was

then passed through a medium porosity glass frit, where the filtrate came through dark

blue; the color persisted about a minute before turning back to pale yellow. Toluene was

then used to extract the product (4 x 30 mL) and the extract was also filtered through a

medium porosity frit to remove any KCl. Like the pentane extract, the solution turned

97

blue coming through the frit and remained that color for a few minutes before returning

to a yellow-orange color. Removal of solvent from the pentane and toluene extracts

(done separately) produced a total yield of 0.134 g (22%) of an oily orange-yellow

product. Attempts to concentrate the solution and grow crystals were unsuccessful.

Attempted synthesis of {(indenyl)manganese(II)chloride(thf)}2,

{(Ind)MnCl(thf)}2. MnCl2 (0.200 g, 1.59 mmol) was added to a 250 mL Erlenmeyer

flask and dispersed in THF (30 mL) by stirring at room temperature for 1 h. Lithium

indenide (0.188 g, 1.54 mmol) was dissolved in THF (50 mL) and added dropwise

through an addition funnel to the flask with MnCl2. The solution turned yellow after a

few drops and gradually turned dark orange after complete addition. The solution was

stirred overnight at room temperature before removal of the solvent under vacuum left a

dark red-orange solid. Pentane was added (20 mL) to extract the product, but the product

was insoluble in pentane and the colorless pentane extract was evaporated to yield a

colorless oil that was likely the coupled indene. An attempt to extract with toluene

yielded a very dark orange solution that produced 0.261 g of an oily orange-red solid

when the toluene extract was filtered and solvent removed under vacuum. Crystallization

attempts were unsuccessful.

Alternate method: MnCl2 (0.297 g, 2.36 mmol) was added to a 250 mL

Erlenmeyer flask and dispersed in THF (50 mL) by stirring at room temperature for 1 h.

Potassium indenide (0.268 g, 2.39 mmol) was dissolved in THF (70 mL) and added

dropwise through an addition funnel to the flask with MnCl2. The orange solution was

allowed to stir overnight at room temperature before removal of the solvent under

vacuum yielded an orange powder. Pentane was added to extract the product, but the

98

product was insoluble in pentane and the colorless pentane extract was evaporated to

yield a colorless oil that was likely the coupled indene. An attempt to extract with toluene

(3 x 30 mL) yielded a dark orange solution that briefly turned green while filtering

through a medium porosity frit, then changed back to orange upon standing. Attempts to

crystallize and isolate the product produced only films and oils that could not be

characterized.

Attempted synthesis of {(indenyl)manganese(II)iodide(thf)}2,

{(Ind)MnI(thf)}2. MnI2 (0.304 g, 0.99 mmol) was added to a 250 mL Erlenmeyer flask

and dispersed in THF (40 mL) by stirring at room temperature for 1 hour. Potassium

indenide (0.153 g, 0.99 mmol) was dissolved in THF (50 mL) and added dropwise

through an addition funnel to the flask with MnI2. The solution turned golden yellow and

was allowed to stir overnight at room temperature. The next morning the solution had

changed to red, and removal of the solvent under vacuum to yielded an orange-red solid.

The product was not soluble in pentane, so it was extracted with toluene (3 x 30 mL) and

filtered through a medium porosity frit (no color change was observed). The toluene was

removed under vacuum to leave 0.280 g (40%) of an oily red solid that could not be

successfully characterized.

Reactions of (indenyl)manganese(II) halides with various gases. Small

amounts (~10 mL) of 10 mM to 50 mM (Ind3Me-2,4,7)MnCl(thf) or (IndMe-2)MnCl(thf) in

toluene or pentane or a mixture of the two were added to a 300 mL pressure vessel inside

a drybox. The vessel was then brought out of the box and put on a Schlenk line where it

was degassed and cooled to -78 °C. The vessel was then pressurized with 20-40 psi of

various laboratory-grade gases (N2, CO, H2, CO2, Ar, and He were all tried) and in every

99

case, the yellow solution gradually turned dark green and eventually a deep royal blue

after a few min. The time necessary to change color could be correlated with the identity

of the gas, as the higher the O2 impurity of the gas, the faster the solutions changed color.

Regular NF grade N2 (<100 ppm O2) displays the fastest change (< 30 sec), followed by

CO (< 10 ppm O2; < 1 min), UHP Ar (< 2 ppm O2; 2-3 min), and eventually Research

Grade N2 (< 0.5 ppm O2; 5 min). Solutions remained blue as long as they were kept

below -20°. Upon warming, the blue color dissipates and the solution usually returns to

its initial color. This can usually be repeated anywhere from 1-6 times before the color

change can no longer be induced by cooling.

The solutions could be opened to vacuum at -78 °C and the blue color would

remain, but upon warming to room temperature, the solutions returned to their initial

yellow color. Attempts to grow crystals of the blue compound at these temperatures by

the removal of solvent produced the original compounds as yellow or orange solids. The

only gas that did not produce this color was O2 itself, which instead turned the solution

brown within seconds of pressurizing with O2 at -78 °C. However, when a degassed

solution was pressurized with a minimal amount of O2 (5 mmol) a color change was

observed in the solution, as a blue color slowly descended from the top of the solution

while the very top of the solution turned brown. The solution exposed to pure O2 does not

remain blue indefinitely, as eventually the solution slowly turns brown after a couple

minutes, even at low temperature. Other attempts to add stoichiometric quantities of O2

have been met with similar results, making it nearly impossible to quantify the amount of

O2 that is actually coordinated at any point in time. One additional feature of these

experiments is that when they are done in THF instead of pentane or toluene, no color

100

changes are observed, suggesting that THF blocks the open coordination site where O2

likely binds.

Reactions of {(Ind3Me-2,4,7)MnCl(thf)}2 with bipyridine, NOBF4, azobenzene,

and tetrathiafulvalene. 1 mM to 10 mM solutions of {(Ind3Me-2,4,7)MnCl(thf)}2 in

pentane or toluene were exposed both to the solid forms of bipyridine (bipy), NOBF4,

azobenzene and tetrathiafulvalene. Bipy, azobenzene and tetrathiofulvalene were also

added dropwise as a solution in toluene or pentane. In the case of bipy, a brown solid was

produced that was soluble in toluene and THF, but could not be characterized. It is

possible that this compound is simply a bipy solvate, where bipy has replaced THF, and

likely taken up any remaining coordination sites on the Mn, or caused the indenyl ligand

to slip to accommodate its coordination. The NOBF4 salt was not soluble in any available

organic solvents, so it was added directly to the solution of {(Ind3Me-2,4,7)MnCl(thf)}2, and

it caused an immediate color change to a deep blue-green color. This color only persisted

for a couple of minutes before the solution turned black and precipitated out an

intractable black tar. This process was repeated at cold temperature (-30 °C), but the

same result was obtained. Addition of azobenzene and tetrathiafulvalene had no visible

or measureable effect on the compound in solution.

Reaction of {(Ind3Me-2,4,7)MnCl(thf)}2 with CO. In order to expose {(Ind3Me-

2,4,7)MnCl(thf)}2 to CO without having O2 present to contaminate the reaction, a method

other than direct CO pressurization had to be attempted. To do this, 20 mL of a 0.10 mM

solution of {(Ind3Me-2,4,7)MnCl(thf)}2 in a 50/50 mix of toluene and pentane was degassed

and cooled to -78 °C in a Schlenk flask. The Schlenk flask was connected to a separate

sealed Schlenk tube that had also been put under partial vacuum and contained solid

101

Co2CO8 (0.189 g, 1.1 mmol). The Co2CO8 was then heated to 50°C, causing it to

decompose into Co4CO12 and CO gas. Excess of CO was used to try and encourage

reactivity. Upon opening the cooled solution of {(Ind3Me-2,4,7)MnCl(thf)}2 to the CO

source, the yellow solution slowly turned a dark maroon color. As with the pressurization

experiments, the color dissipated upon warming. An IR spectrum of the maroon solution

appeared the same as {(Ind3Me-2,4,7)MnCl(thf)}2; there was no evidence for a CO stretch.

Results

Mono(indenyl)manganese(II) halide complexes were synthesized by salt

metathesis elimination reactions of the appropriate indenide salts with MnX2 in THF (5).

2 K[Ind´] + 2 MnX2 {Ind´MnX(thf)}2 + 2 KX↓ (X = Cl or I) (5)

After the removal of THF under vacuum, addition of pentane or toluene served to

extract the manganese complexes, allowing for the removal of the alkali metal chloride

by-products. The purified (indenyl)manganese complexes were crystallized by cooling

of a concentrated solution to approximately -30 °C. They are lighter in color than their

bis(indenyl) counterparts and tend to be green-yellow in color for the chlorides, and dark

green for the iodide. Again, it should be stressed that the preparation of the indenyl

complexes requires chemicals and reagents of very high quality (e.g. MnCl2 beads of

>99.99% purity) in order to yield consistent results. These compounds are also highly

air- and moisture-sensitive, like their bis(indenyl) counterparts. For {(Ind3Me-

2,4,7)MnCl(thf)}2, the solid-state magnetic moment was also determined by SQUID

magnetometry, and was fit to an extension of the Bleaney-Bowers equation.177,178 The

102

data obtained was consistent with anti-ferromagnetic coupling between two high-spin

Mn(II) (S = 5/2) centers (g = 2.04, J/kB= -17.7 K). The magnetic moment in toluene d8 is

7.3 µB, which is consistent with the room temperature magnetic susceptibility obtained

by SQUID magnetometry (7.74 µB).


[(Ind3Me-2,4,7)MnCl(thf)]2. Crystals of [(Ind3Me-2,4,7)MnCl(thf)]2 were harvested as

green-yellow rods from a cold pentane solution. An ORTEP of an expanded asymmetric

unit for the polymeric molecule is shown in Figure 58, which gives the numbering

scheme that is referred to in the text. Selected bond lengths and angles are shown in

Table 4.

There is an inversion center between the two manganese centers, making only

half of the molecule unique. Cp analogues of this dimeric structure are known, [1,2,4-

(tBu)3CpMnCl(thf)]242 and [(CH3C5H4)MnCl(PEt3)]2.62 Like these compounds, the

indenyl compound features bridging chlorides with Mn-Cl distances of 2.483 Å and

2.424 Å for each manganese to the two chloride atoms. These distances are comparable

to those in the Cp analogues. The Mn…Mn distance is noticeably shorter (3.386 Å

compared to 3.514 Å), but is still outside of usual Mn…Mn bonding distances.20 The

indenyl ligand appears to show a slipped η2 interaction, but the rest of the ring is still

within range of what has previously been considered bonding. When viewed

orthogonally to the C5 plane, the Mn atom is shifted towards the C1 carbon of the ring, as

opposed to the C2 carbon as is often expected when slippage occurs. Despite appearing

103

to be an η2 interaction, the ring is still clearly delocalized, as the C-C distances of the

five-membered ring are all within 0.03 Å of one another.

Table 4. Selected bond distances for [(Ind3Me-2,4,7)MnCl(thf)]2.


Mn(2)–C(19) 2.325(2) C(18)–C(19) 1.409

Mn(2)–C(18) 2.382(2) C(19)–C(25) 1.432

Mn(2)−C(17) 2.525(2) C(25)−C(24) 1.437

Mn(2)−C(24) 2.624(2) C(24)−C(17) 1.418

Mn(2)−C(25) 2.492(2) C(17)−C(18) 1.400

Avg. Mn–C 2.470(5) Mn(2)−Cl(2) 2.4237(5)

Mn…Mn 3.380(2) Mn(2)−Cl(2b) 2.4832(6)

ΔMn−C = 0.299

Figure 58. Diagram of the non-‐hydrogen atoms of [(Ind3Me-2,4,7)MnCl(thf)]2 with the numbering scheme used in the text. Thermal ellipsoids are shown at the 50% probability level.

104

[(IndMe-2)MnI(thf)]2. Crystals of [(IndMe-2)MnI(thf)]2 were harvested as dark

green blocks from a cold mixture of toluene and hexanes (2:1). An ORTEP of an

expanded asymmetric unit for the dimeric molecule is shown in Figure 59, which gives

the numbering scheme that is referred to in the text. Selected bond lengths and angles are

shown in Table 5.

As with the structure of [(Ind3Me-2,4,7)MnCl(thf)]2, the compound has an inversion

center that makes only half of the molecule unique, but instead of the two bridging

chlorides, the compound contains two bridging iodides. The Mn…Mn distance has

increased to 3.668 Å from the 3.386 Å in [(Ind3Me-2,4,7)MnCl(thf)]2, but that is to be

expected due to the increased size of the bridging iodine atoms. A similar increase is

observed in the change in the Mn-X bond distances, as the Mn-I distances are 2.792(3) Å

and 2.831(3) Å compared to the 2.424(1) Å and 2.483(1) Å observed in the chloride-

bridged complex. There is only one previous example of a similar organometallic MnII

complex with bridging iodides, [MeCpMnI(PEt3)]2, and it displays both longer Mn-I

(2.865 Å) and Mn…Mn (3.952 Å) distances. However, this difference is consistent with

the difference in ligand sets between [MeCpMnCl(PEt3)]2 and [Ind3Me-2,4,7MnCl(thf)]2.

The indenyl ligands appear to display an unusual type of η3 coordination. The Mn

center is usually bound to the carbons in the 1-, 2-, and 3-postitions of the indenyl ring

and is centered roughly over C(2) when the indenyl group is η3 coordinated. However, in

this case, the Mn center is clearly shifted towards C(1) with a bond distance of 2.331(2)

Å, almost a full 0.1 Å shorter than the distance to C(2) (2.427(2) Å). As a further

indication of an η3 interaction, the difference in Mn-C distances between the average of

these 3 carbons and the remaining 2 carbons is about 0.18 Å. To our knowledge this

105

would be the first time an indenyl group has shown this type of side-on η3 conformation.

However, despite the difference in Mn-C bond lengths, the Mn-C(3) and Mn-C(9)

distances are still both within distances previously considered to be bonding for other η5

bound Mn(II) complexes.

Table 5. Selected bond distances for [(IndMe-2)MnI(thf)]2.


Mn(1)–C(1) 2.331(2) C(1)–C(2) 1.422

Mn(1)–C(2) 2.427(2) C(2)–C(3) 1.411

Mn(1)−C(3) 2.553(2) C(3)−C(9) 1.426

Mn(1)−C(9) 2.618(2) C(9)−C(8) 1.442

Mn(1)−C(8) 2.467(2) C(8)−C(1) 1.435

Avg. Mn–C 2.479(5) Mn(1)−Cl(1) 2.792(1)

Mn…Mn 2.291(3) Mn(1)−Cl(1a) 2.831(1)

ΔMn−C = 0.287

106

Figure 59. Diagram of the non-‐hydrogen atoms of [(IndMe-2)MnI(thf)]2 with the numbering scheme used in the text. Thermal ellipsoids are shown at the 50% probability level.

Spectroscopic Results

FTIR Spectroscopy

In an effort to observe the presumed oxygen-bound species of [IndMe-

2MnCl(thf)]2, solution IR spectra were collected for a 10 mM solution of the yellow

[IndMe-2MnCl(thf)]2, and for the same solution after having turned dark blue when cooled

to -45 °C in the glovebox freezer (Figure 60). The spectrum of the cold [IndMe-

2MnCl(thf)]2 solution shows a slight change from the initial room temperature spectrum

of [IndMe-2MnCl(thf)]2, with the major difference being the formation of a new peak at

1119 cm-1 (Figure 62). This is in the range commonly associated with superoxide O−O

stretches, suggesting the oxidation of MnII to MnIII. Due to the fact that the initial

complex is a dimer, it is also possible that the IR band at 1119 cm-1 corresponds to a

peroxo species where the O22- group is bridging between the two manganese centers, both

of which have oxidized to MnIII. This experiment was attempted for [Ind3Me-

107

2,4,7MnCl(thf)]2 , but the blue species would not persist long enough in solution to

transport the solution cell from the glovebox freezer to the instrument, despite several

precautions that were taken to prevent this.

Figure 60. Comparison of IR spectra for [IndMe-2MnCl(thf)]2 at room temperature (blue spectrum) and the presumed oxo-species at cold temperature (red spectrum)

UV-vis Spectroscopy

To monitor and attempt to quantify the vivid color change that occurs upon

cooling [Ind3Me-2,4,7MnCl(thf)]2 in the presence of trace levels of oxygen, electronic

absorption spectroscopy (UV-vis) was performed. To do this, a 10 mM sample of

[Ind3Me-2,4,7MnCl(thf)]2 was prepared in toluene and then sealed in a quartz cuvette inside

a nitrogen atmosphere glovebox. The sample was then brought outside the box and

placed in a UV-vis spectrophotometer with a cryostat to regulate the temperature. Two

different experiments were conducted; in the first, the sample was slowly cooled from

room temperature to -60 °C in 10° C intervals every 5 minutes while monitoring the

corresponding change in the UV-vis spectrum. In the second experiment, the complex

was immediately placed in the cryostat that was cooled to -60 °C and the UV-vis

108

spectrum of the solution was collected every 5 minutes until the absorbance stopped

rising (Figure 61). This figure shows the slow increase in absorbance at 643 nm over

time (showing spectra from 20 minute intervals) while the solution remains cooled at –

60 °C. The increase in intensity of this peak indicates an increase of the oxygen

containing species present in solution.

The only major problem with interpreting these spectra is that there is no way to

quantify how much of the initial manganese complex is binding O2. The first problem

encountered in trying to do so involves attempting to fully degas the solution once inside

the cuvette, as even a supposedly clean nitrogen atmosphere glove box possesses the

requisite oxygen concentrations to initiate the color transition at low temperatures. The

cuvettes cannot be freeze-pump thawed, and pulling a vacuum on the non frozen solution

will eventually pull off solvent, changing the solution concentration, and hence

preventing accurate calculations of observable electronic properties such as molar

absorptivity. Attempts were made to syringe in controlled amounts of both air and O2,

but in both instances, the complex quickly turned blue and then brown and the blue color

did not persist. If the molar absorptivity were calculated for this compound, assuming all

of the Mn had bound oxygen, it would be 250 M-1 cm-1. The real value is likely slightly

higher, given that not all of the initial complex may have reacted to form the colored

species. Other manganese superoxide and peroxide systems have shown similar values

for the extinction coefficient ranging anywhere from 70 M-1 cm-1 to 700 M-1 cm-1. 175

109

Figure 61. UV-vis spectra for [Ind3Me-2,4,7MnCl(thf)]2. Observed λmax at 643 nm consistent with either a superoxido- or a peroxidomangnaese compound.

Resonance Raman

Resonance Raman (rR) studies were performed on [Ind3Me-2,4,7MnCl(thf)]2 and its

resulting blue oxo-species formed at low temperature. A full excitation profile has been

done on both the starting material and the blue oxo-species it forms. Thus far the only

results that have been sent to us from our collaborators at the Que lab at the University of

Minnesota are for the spectra collected from the excitations at 647 nm. This is near the

λmax observed for the oxo species in the UV-vis.

The rR of the oxo-species is very rich, but the fact that there are so many peaks

when comparing the blue complex to the starting material (Figure 62) suggests that most

0

0.5

1

1.5

2

2.5

3

300 400 500 600 700 800 900 1000 1100

Absorbance

Wavelength (nm)

UV-vis Spectra of 10 mmol {Mn(2,4,7-Me3C9H4)Cl(thf)}2 at -60 °C

Spectra collected every 20 min λmax ≈ 643 nm

110

of the peaks are likely to be ligand-based. Had 18O been available to do 18O labeling

studies, it would be possible to easily determine which peaks are ligand based and which

are O−O and Mn−O based. All spectra were normalized to toluene at 621 cm-1. More

definitive information on the oxo-species should be available once the excitation profile

is fully analyzed, and the Mn−O peak frequencies should give an indication of the type of

Mn−O bonding present.

Figure 62. Resonance Raman spectra for the blue oxo-species and the [Ind3Me-

2,4,7MnCl(thf)]2 starting material at an excitation wavelength of 647nm. Peaks labeled “S” are those of the solvent toluene. Asterisks (*) indicate peaks unique to the oxo-species.

111

EPR Spectroscopy

Low temperature X-band EPR spectroscopy was performed on [Ind3Me-

2,4,7MnCl(thf)]2 (Figure 63), its associated blue oxo-species (Figures 64 and 65), and the

decomposition products formed when the oxo-species is warmed (causing the solution to

turn brown before being refrozen). There is a stark difference in the spectrum of the blue

oxo-species in comparison to the initial [Ind3Me-2,4,7MnCl(thf)]2 starting compound

(Figure 64). The spectrum of the starting compound is shown below (Figure 63) and

contains multiple signals, the clearest two of which have g-values of 4.439 and 3.264.

The hyperfine splitting in these signals is exceptionally complicated, as [Ind3Me-

2,4,7MnCl(thf)]2 contains two I = 5/2 55Mn centers. However, the fact the compound is

dimeric with two antiferromagnetically coupled MnII centers makes it surprising [Ind3Me-

2,4,7MnCl(thf)]2 even has an EPR signal a low temperature (10 K). The signal centered at

g = 4.439 is less defined than the one centered at 3.264, which shows much clearer

hyperfine splitting; however, it appears as though there are two sets of overlapping six-

line hyperfine splitting, each with A ≈ 60 G. It is more difficult to decipher the hyperfine

of the signal at g = 4.439, as it appears there are multiple six-line splittings present as

with the signal at g = 3.264, but it could also be a slightly distorted eleven-line spectrum,

which one might expect for a compound with 2 I = 5/2 55Mn centers.

112

Figure 63. EPR spectrum of [Ind3Me-2,4,7MnCl(thf)]2. T = 10 K, Freq = 9.65 GHz, Power = 0.2 mW. Full spectrum (top left) and enlarged views of the signals at g = 4.439 (top right), g = 3.264 (bottom left), and potential signals with g < 2.

It is possible that since the signal for [Ind3Me-2,4,7MnCl(thf)]2 is relatively weak,

that the complex responsible for the EPR signal is not [Ind3Me-2,4,7MnCl(thf)]2, but instead

(Ind3Me-2,4,7)2Mn, which as mentioned in the introduction, is also present in a solution of

[Ind3Me-2,4,7MnCl(thf)]2.

The spectrum of the oxo-species is much more intense, and has more defined

hyperfine splitting. There are signals centered at g = 9.367, g = 4.405, and g = 3.675 that

all display hyperfine splitting. The first and last of these display six-line hyperfine

splitting patterns with A values of 49 G and 54 G for the signals at g = 9.367 and g =

3.675, respectively. This slight decrease in the hyperfine splitting compared to the initial

compound could potentially indicate an oxidation state change in the Mn center from

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MnII to MnIII. The signal at g = 4.405, on the other hand, shows a very complicated,

potentially eleven-line, hyperfine pattern that has an approximate A value of 26 G. This

is extremely small for a manganese system, suggesting maybe this is actually two

overlapping six-line patterns, as in the initial compound. The problem with this

assignment is the peak intensities do not seem consistent with what would be expected

for two overlapping six-line splitting patterns, which is what appears to be the case for

the signal near g = 3.264 for the initial compound. There is may be additional signals

with g < 1.8, but they are not strong and do not display any noticeable hyperfine splitting.

The last major feature in the spectrum is the presence of a signal that is not associated

with Mn, observed near g = 2. This likely corresponds to the presence of a superoxide.

There was no 17O available to try and generate an isotopically labeled oxo-species to

observe a splitting on this signal from the I = 5/2 17O center.

114

Figure 64. EPR spectrum of oxo-species of [Ind3Me-2,4,7MnCl(thf)]2 (top) and a comparison of the oxo- (red) and initial species (green) (bottom). T = 10 K, Freq = 9.65 GHz, Power = 0.2 mW.

115

Figure 65. Enlarged views of the EPR signals of blue oxo-species of [Ind3Me-

2,4,7MnCl(thf)]2 centered at g = 9.367 (top left), g = 4.405 (top right), g = 3.675 (bottom left), and g ≈ 2 (bottom left).

Discussion

Despite [Ind3Me-2,4,7MnCl(thf)]2 originally being isolated as a by-product while

trying to make the bis(indenyl)manganese compound, substituted (indenyl)manganese(II)

halides have provided a rich amount of interesting solution chemistry in the presence of

trace quantities of oxygen.

This chemistry was first witnessed while attempting to crystallize a sample of

[Ind3Me-2,4,7MnCl(thf)]2. A small amount of the yellow/orange solid that had been cooled

to -10 °C was redissolved in pentane at room temperature, only to have the resulting

116

solution instantly turn dark green; upon warming the green color changed back to yellow.

Various hypothesis for the color change were proposed and tested along several lines.

The first possibility to be explored involved the potential for a spin-crossover

compound as a cause for the observed color change. However, the possibility of a spin-

state change being the cause was diminished when SQUID based magnetic data revealed

there was no spin crossover occurring in the compound’s solid state. Spin-crossover

behavior would be even less likely to occur in solution as it is easier for intermolecular

interactions to occur between atoms/molecules in the solid state. This result rendered

unlikely the hypothesis that the color change was due to a spin-crossover phenomenon.

Evan’s method was used to measure the magnetic susceptibility in solution, and while the

compound still appeared to be in the high spin state at room temperature, variable

temperature (VT) experiments gave very peculiar results. They indicated a potential

increase in magnetic moment with decreased temperature. However, these results were

later proved erroneous as the sample had its spectra taken at low temperature first, and

the compound decomposed as the temperature was raised. EPR data would later show the

decomposition products are EPR silent, potentially suggesting a reduced number of

unpaired electrons, and offering an explanation for the confusing VT NMR results.

The second possible cause that was examined was that the compound was simply

thermochromic. Degassing a solution of [Ind3Me-2,4,7MnCl(thf)]2 and then cooling it to -78

°C showed that thermochromism was not the cause of the color change, however. This

result, coupled with the previous one ruling out a spin state change, combined to suggest

that a chemical reaction causes the color change. Further evidence for this was found

when a solution of [Ind3Me-2,4,7MnCl(thf)]2 in THF was cooled to -78 °C without being

117

degassed, and failed to show a color change. If the cause of the color change were a

chemical reaction, then this result can be explained by the THF solvent coordinating to

any accessible sites on the Mn centers, preventing any reactive species from subsequently

binding to the metal center.

The possibility that [Ind3Me-2,4,7MnCl(thf)]2 might reversibly bind the dinitrogen

gas of the glove box atmosphere was then considered. A solution of (Ind3Me-

2,4,7)MnCl(thf) in toluene was degassed and pressurized with N2 at room temperature,

resulting in a slight color change at the solution’s surface from yellow to green. Upon

further cooling in an ice bath at 0 °C the solution turned dark green, and further cooling

to -78 °C turned the solution a deep royal blue color. Whether the color change was

unique to N2 binding was examined by testing a series of gases under similar conditions.

After repeating the same experiment with CO, H2, N2O, CO2, Ar, and He and achieving

the same color change each time, it was concluded there was likely a common

contaminant responsible for the color change, probably elemental oxygen. This should

not be too surprising as carbonyl complexes of MnII are unknown, as are dinitrogen

compounds of MnII. This is a consequence of the absence of an empty orbital in high-

spin MnII to accept a lone pair of electrons from N2 or CO, making binding unlikely

without a spin state change, which the SQUID data had already ruled out.

Once it became evident that oxygen was the likely cause, an FTIR experiment

was conducted to see if an O−O band could be seen. When spectra of the initially yellow

[Ind3Me-2,4,7MnCl(thf)]2 and its presumed blue oxo-species were taken and compared,

there was an additional peak at 1119 cm-1 in the spectrum of the blue solution. This value

is consistent with transition metal superoxide compounds, which are generally found

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between 950-1200 cm-1.173 In addition, previously documented superoxido- and peroxo-

manganese complexes have been reported as being green and blue in color.171,175 This is

of importance because it should be noted that blue and green are not common colors for

MnII organometallic complexes, which tend to be yellow or orange in color. A charge

transfer between O2 and a MnII center to form a superoxide and MnIII metal center would

explain the intense color change.

Further characterization of the oxo-species proved exceedingly difficult due to the

strict conditions required for the compound to form, but not immediately decompose. It

was found that the complex only persisted at low temperatures (below -40 °C), but more

importantly, that slightly increased oxygen levels caused decomposition, even at low

temperature. Having a finite window of oxygen concentrations (on the single ppm scale)

where this phenomenon could be observed made for challenging characterization due to

the difficulty in handling and manipulating the compounds. Thus, a collaboration with

the Que lab at the University of Minnesota was sought to help with further

characterization. With the aid of the Que lab, UV-vis, resonance Raman and EPR

experiments were conducted in attempt to better characterize the oxo-species being

formed by [Ind3Me-2,4,7MnCl(thf)]2.

Electronic absorption spectroscopy showed the formation of a new peak with λmax

= 643 nm. This is similar to what is seen for other peroxide and superoxide compounds

of manganese, which also typically display an additional feature near 400-450 nm.170,171

This second feature was not observed in this case due to the presence of strong

absorbance in this region from indenyl ligand, which absorbs heavily in that region. The

approximate extinction coefficient observed for the blue oxo-species is 250 M-1 cm-1.

119

This is consistent with what has been observed for other superoxo and peroxo species of

manganese.175

The EPR spectra of both the initial complex and the oxo-species are fairly

complex, but there is clear evidence of a drastic electronic change. Specifically, it

appears that the initial compound, which is initially dimeric, has become monomeric in

the new oxo-species. This is evidenced by the very clear six-line hyperfine structures

with average splittings of 49 G and 54 G, which, coupled with the resonance locations,

suggest a monomeric 55MnIII center. There is also the presence of a signal near g = 2 that

is not from unpaired electron density on manganese, as it lacks any hyperfine splitting.

The only possible spots for this unpaired electron density to be found if it is not located

on Mn are the indenyl ligand or newly formed superoxide. The assignment of a

superoxide for this EPR signal matches what is observed for the O−O stretch in the IR.

For full characterization, however, EPR spectral simulations will be required to confirm

this assignment.

Full resonance Raman interpretation is still forthcoming, as the substituted

indenyl ligand has a large number of vibrations that show up in the spectra and must be

accounted for. Without the benefit of an 18O labeled experiment, it is very difficult to

identify the exact peaks corresponding to a Mn−O interaction. The preliminary Raman

data from excitation at 647 nm was given in the results section, but without the rest of the

excitation profile, an assignment of the Mn−O bond is not possible. Since [Ind3Me-

2,4,7MnCl(thf)]2 does not absorb at 647 nm (based on its UV-vis spectrum), the full extent

of ligand vibrations is not obvious, requiring that a full excitation profile over the visible

spectrum be obtained.

120

Conclusions

In addition to having synthesized the bis(indenyl)manganese(II) compounds

described in Chapter III, mono(indenyl)manganese(II) halides can also be synthesized.

While possessing some similarities to the analogous bis(indenyl) complexes, the

mono(indenyl)manganese halides show a marked difference in their chemical behavior.

In particular is the fact that [Ind3Me-2,4,7MnCl(thf)]2, [IndMe-2MnCl(thf)]2, [IndMnCl(thf)]2,

and [IndMe-2MnI(thf)]2 all display reactivity with elemental oxygen that be observed in the

presence of only single ppm levels of O2. It should be noted that attempts to form [Ind2Me-

4,7MnCl(thf)]2 were unsuccessful, as only the bis(indenyl) complex was formed.

Additionally, complexes with larger frontside steric bulk on the indenyl ligand, such as in

[Ind3Me-1,2,3MnCl(thf)]2 or with any trimethylsilylated species, do not display this type of

behavior with oxygen.

The sensitivity of these complexes to elemental oxygen is of specific interest, as

the interaction can be observed even under normal glove box conditions. That kind of

sensitivity lends itself to use as a potential oxygen sensor, as neither trimethylaluminum

nor diethyl zinc react with such levels of oxygen. The nature of the interaction can at this

point best be described as the formation of a MnIII superoxide compound. The final

results of the resonance Raman, coupled with EPR simulations, will help to either

confirm this assignment or offer new evidence of another assignment.

121

CHAPTER V

SYNTHESIS AND CHARACTERIZATION OF MANGANGESE(II)

COMPLEXES OF BULKY ARYLOXIDES

Introduction

While metal alkoxides have been known for over a century, dating from the first

synthesized alkoxides of aluminum in the late 1800s,179 metal alkoxides attracted

increasing attention starting in the 1980s. It was at this time they were observed as

intermediates in processes such as hydrogenation of aldehydes and ketones and the

carbonylation of olefins.180,181 In addition, these compounds have been recognized for

their potential use as precursors for chemical vapor deposition (MOCVD) of metal oxide

films.182-184 However, applications of these compounds are limited by their air and

moisture sensitivity. One way to address these sensitivity issues involves the use of

bulkier aryloxide ligands to block decomposition pathways.

In the case of manganese, there are only a few of these aryloxide compounds that

have been synthesized and structurally characterized that do not possess chelating

functional groups on the aryl ring.185-189 Often, the chelating atom is not C, H, or O,

which can potentially restrict use in MOCVD due to the impurities that could be left

behind by heteroatoms. However, there are additional uses for aryloxide compounds. In

the case of simple phenoxides, there is interest in their ability to assist the conversion of

acylmanganese to alkoxy carbonyl derivatives via treatment with syn gas. Additionally,

bipy solvated manganese(II) aryloxide dimers display both intramolecular and

intermolecular ferromagnetism in the solid state.185 There are even some pyridyl

substituted phenoxides of manganese that are capable of enzymatic-like behavior.189

122

There are a variety of ways to prepare metal alkoxides and aryloxides, most of

them involving the reactions of alcohols, phenols, or phenoxide ions with metal amides

or halides. A newer approach, introduced by Deacon et al,187 synthesizes monomeric

manganese phenoxides via the reaction of manganese powder, Hg(C6F5)2, and substituted

phenols in the presence of trace mercury in dimethoxyethane (DME). This reaction is

claimed to be an efficient one-pot synthesis that takes place via protolytic ligand

exchange and gives the monomeric manganese phenoxides in moderate to good yields

(40-70%). Despite the reasonable yields, the toxicity associated with both

perfluorophenyl mercury(II) and mercury itself make this a less than desirable route.

The preparation of aryloxide complexes of MnII became of interest in our lab

upon the isolation of a dimeric (indenyl)manganese compound that contained a

deprotonated bridging butylhydroxytoluene (BHT) group, (IndMe-2)2(µ-IndMe-2)Mn2(µ-

BHT). This was only the second example of an organometallic species that also

contained an aryloxide coordinated to the same metal center. While attempts to make

additional aryloxide-containing organometallic complexes were unsuccessful, we report

the synthesis of new manganese(II) phenoxides that can be prepared by a simple salt

metathesis reaction between a manganese(II) halide and the potassium salt of the

substituted aryloxide.

Experimental




123






Alfa Aesar and used as received. 2-methylindene, n-butyl lithium, potassium

bis(trimethylsilyl)amide, 2,6-diisopropylphenol, butylhydroxytoluene, anhydrous

pentane, and anhydrous, unstabilized tetrahydrofuran (THF) were purchased from

Aldrich and used as received. Hexanes, toluene, and diethyl ether were distilled under

nitrogen from potassium benzophenone ketyl. Toluene-d8 (Aldrich) was vacuum distilled

from Na/K (22/78) alloy and stored over type 4A molecular sieves prior to use.







elsewhere.149






124



Madison, WI).




collection.








Synthesis of potassium 2,6-di-tert-butyl-4-methylphenoxide, K[2,6-(C(Me3)2)-

4-Me-C6H2-2-O], KBHT. 2,6-di-tert-butyl-4-methylphenol (1.049 g, 4.76 mmol) was

dissolved in toluene (30 mL) in a 250 mL Erlenmeyer flask. Potassium

bis(trimethylsilyl)amide, K[N(SiMe3)2], (0.908 g, 4.55 mmol) was dissolved in toluene

(20 mL) and added dropwise to the phenol solution while stirring. The solution

immediately slowly turned to an opaque milky white color upon the addition of the

potassium bis(trimethylsilyl)amide. After stirring for 24 h at room temperature, the

solution became yellow-green. Hexanes (150 mL) were then added to fully precipitate

the potassium phenoxide salt, which was then filtered over a medium-porosity frit,

125

washed with hexanes, and dried under vacuum to yield 0.849 g (72.2%) of a white

powder that confirmed to be the phenoxide salt by 1H NMR (300 MHz) in C6D6: δ 1.38

(singlet, 18H, C(CH3)3); 2.07 (singlet, 3H, CH3); 6.62 (singlet, 2H, CH in 3,5-position).

Synthesis of potassium 2,6-diisopropylphenoxide, K[2,6-(CH(Me2)2)-C6H3-2-

O], KODipp. 2,6-diispropylphenol ( 3.061 g, 17.1 mmol) was dissolved in toluene (25

mL) in a 250 mL Erlenmeyer flask. Potassium bis(trimethylsilyl)amide, K[N(SiMe3)2],

(3.261 g, 16.3 mmol) was dissolved in toluene (20 mL) and added dropwise to the phenol

solution while stirring. The solution slowly darkened to a grayish color, and became very

thick. The rate of addition had to be slowed to prevent stirring from being stopped.

Additional toluene (15 mL) was added to keep solution stirring overnight at room

temperature. By the next morning, the solution was still thick and gray in color, but with

the addition of hexanes (175 mL) it became more white and much less viscous. A white

precipitate was formed and vacuum filtered to produce 3.208 g (86.7%) of a white

powder that was confirmed to be the phenoxide salt by 1H NMR (300 MHz) in THF-d8: δ

1.12 (doublet, 12H, CH(CH3)2); 3.50 (quintet, 2 H, CH(CH3)2); 6.50 (triplet, 1H, CH in

4-position); 6.68 (doublet, 2H, CH in 3,5-positions).

Attempted synthesis of (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT). Multiple attempts

were made to remake this compound intentionally and are described here. Method I.

Anhydrous MnCl2 (0.210 g, 1.67 mmol, 1 eq) was added to a 250 mL Erlenmeyer flask

and stirred for 1 h in THF (50 mL) to disperse the MnCl2. Potassium 2-methylindenide

(0.425 g, 2.53 mmol, 1.5 eq) and BHT (0.184 g, 0.835 mmol, 0.5 eq) were dissolved in

THF (85 mL) at room temperature and added dropwise into the flask containing MnCl2.

The resulting reaction mixture immediately turned yellow upon addition, and was

126

allowed to stir overnight at room temperature, after which the solution had turned bright

red. The solvent was then removed under vacuum, leaving a light yellow solid. The

product was extracted with pentane (3 x 30 mL) and decanted into a medium porosity

glass frit. The solution turned green upon filtering, indicating presence of the oxo species

of [(IndMe-2)MnCl(thf)]2. Pentane was then removed under vacuum to leave 0.335 g of a

yellow solid. This solid was redissolved in pentane and cooled to 0 °C, which caused the

crystallization of pale yellow needles. 1H NMR of the needles contained only broad,

structurally uninformative, signals due to the presence of paramagnetic MnII. Crystals

likely desolvated before an X-ray structure could be obtained. Attempts to grow crystals

from pentane at 0 °C produced olive green blocks that did not diffract. Method II.

Anhydrous MnCl2 (0.827 g, 6.57 mmol, 1 eq) was added to a 250 mL Erlenmeyer flask

and stirred for 1 h in THF (40 mL) to disperse the MnCl2. Potassium 2-methylindenide

(1.659 g, 9.86 mmol, 1.5 eq) and KBHT (0.849 g, 3.29 mmol, 0.5 eq) were dissolved in

THF (40 mL) at room temperature and added dropwise into the flask containing MnCl2.

The resulting reaction mixture immediately turned a brownish orange upon initial

addition, before becoming olive green after complete addition. The reaction mixture was

allowed to stir overnight at room temperature, after which the solution had turned bright

red. The solvent was then removed under vacuum, leaving a brown-orange solid. The

product was extracted with pentane (3 x 30 mL) and poured over a medium porosity glass

frit to filter off KCl. No color changes were observed upon filtration, and the filtrate was

a very dark orange color. After standing at room temperature for 72 hours, large, pale,

orange-yellow blocks (80 mg) crystallized that were suitable for single crystal X-ray

analysis. The resulting compound proved not to be the expected (IndMe-2)3Mn2(BHT), but

127

instead a dimeric manganese phenoxide that featured both bridging and terminal

phenoxide groups, and a bridging chloride. Synthesis of this compound from the

stoichiometric combination of appropriate reagents is described below. Method III.

Bis(2-trimethylindenyl)manganese (0.184 g, 0.587 mmol) was dissolved in THF (30 mL)

to give a red solution that was stirred while KBHT (0.077 g, 0.298 mmol) in THF (10

mL) was added dropwise via pipet over 5 min. No color change was visible during or

immediately after addition. After 16 h the solution had darkened slightly in color, and the

THF was removed under vacuum, leaving a pale pinkish-red solid. Pentane (1 x 30 mL)

and toluene (2 x 30 mL) were used in attempt to extract the product, but the product did

not appear to be soluble in pentane, and the dark orange filtrate of the toluene yielded

only an intractable orange-red oil.

Synthesis of [Mn(BHT)(THF)]2(µ-BHT)(µ-Cl). MnCl2 (0.285 g, 2.27 mmol, 2

eq) was added to a 250 mL Erlenmeyer and dispersed in THF (75 mL) by magnetic

stirring for 1 hour before adding KBHT (0.887 g, 3.43 mmol, 3 eq) in THF (50 mL)

dropwise. The solution initially turned yellow-orange before becoming a dark rose color.

After stirring overnight, the solvent was removed under vacuum to yield a red solid that

was extracted with pentane (3 x 30 mL) and filtered over a medium porosity glass frit,

producing a pale, rosy pink filtrate. The pentane filtrate was then removed under vacuum,

leaving 0.880 g (76%) of a pale orange solid, mp 198-208 °C (dec). Anal. Calcd. for

C58H97O5Mn2Cl: C, 67.16; H, 9.05; Mn, 11.60; Cl, 3.74. Found: C, 66.39; H, 9.09; Mn,

11.66; Cl, 3.95.

Attempted synthesis of bis(2,6-diisopropylphenoxy)-manganese(II),

(KODiPP)2Mn(thf)x. MnCl2 (0.257 g, 2.04 mmol) was added to a 250 mL Erlenmeyer

128

and dispersed in THF (40 mL) by magnetic stirring for 1 hour before adding KODIPP

(0.864 g, 3.99 mmol) in THF (40 mL) dropwise. The solution initially turned light brown

before ending up a greenish-gray color. After stirring overnight, the solvent was removed

under vacuum to yield a brown-black solid that was extracted with pentane (2 x 30 mL)

and then toluene (1 x 40 mL). Both fractions were filtered over a medium porosity glass

frit, producing dark brown filtrates. The solvents were both removed under vacuum,

leaving a total of 0.609 g (73%) of dark green-gray solid, mp 162-166 °C (dec).

Results and Discussion

New manganese(II) aryloxide species have been prepared by straightforward salt

metathesis elimination reactions of MnCl2 and the appropriate amounts of potassium

phenoxide salts. These compounds can be extracted using pentane or toluene following

the removal of THF and the alkali metal by-products. Purified solutions of the

manganese aryloxide species in pentane gave crystals at room temperature upon slowly

allowing the solvent to evaporate.


(IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT). (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) was

isolated from the reaction of MnCl2 and 2 equivalents of IndMe-2 in anhydrous THF

containing BHT as an inhibitor. Yellow plate like crystals of (IndMe-2)2(µ-IndMe-2)Mn2(µ-

BHT) were obtained from a pentane solution. A plot of the molecule is shown below in

Figure 66.

129

Deprotonated butylhydroxytoluene (BHT) is present in the molecule as a bridging

ligand. The average Mn−O distance is 2.045(4) Å, which is on the low end for distances

seen in similarly bridging aryloxide complexes of MnII (2.07-2.20 Å).189-191 This distance

is still considerably longer than the Mn−O bonds seen for terminally bound aryloxides,

however, which typically range from 1.86-1.95 Å.186,187

The molecule also contains two terminal and one bridging 2-methyindenyl group.

The terminal groups appear to have a slipped η5-coordination, similar to what is observed

for the methylated (indenyl)manganese halides from Chapter IV. The average distance is

2.48(2) Å for all 10 Mn-C bonds, which is only slightly longer than what is considered η5

coordination in other compounds.139 The amount of slippage (Δ(Mn-C) = 0.198 Å) is

also slightly less than that usually expected for an η3-C5 ring.19 The visible centering of

the manganese atom is towards the front portion of the ring when looking from a view

orthogonal to the C5 plane, suggesting possible η3-coordination.

The bridging 2-methylindenyl ligand is clearly η1-bound to both manganese

atoms. The distances of the 1- and 3-positions to the metal centers to which each is

coordinated are 2.259192 and 2.282192 Å, while the distances to the bridgehead carbons or

the carbon in the 2-position are all greater than 2.95 Å from both metal centers. The

Mn(1)-Mn(2) distance in the complex is 3.56 Å, which is well beyond the range of metal-

metal bonding.20

130

Table 6. Selected bond distances for (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT).


Terminal Bridging

Mn(1)–C(1) 2.390(1) Mn(1)–C(19) 2.259(1)

Mn(1)–C(2) 2.353(1) Mn(2)–C(21) 2.282(2)

Mn(1)−C(3) 2.413(1) C(1)−C(2) 1.412(1)

Mn(1)−C(9) 2.576(2) C(2)−C(3) 1.413(1)

Mn(1)−C(8) 2.558(2) C(3)−C(9) 1.427(1)

Avg. Mn(1)–C 2.458(3) C(9)−C(8) 1.435(1)

Mn(2)–C(10) 2.416(2) C(8)−C(1) 1.436(1)

Mn(2)–C(11) 2.385(3) C(10)−C(11) 1.409(1)

Mn(2)−C(12) 2.448(1) C(11)−C(12) 1.408(1)

Mn(2)−C(18) 2.637(1) C(12)−C(18) 1.437(1)

Mn(2)−C(17) 2.625(1) C(18)−C(17) 1.446(1)

Avg. Mn(2)–C 2.502(4) C(17)−C(10) 1.460(1)

ΔMn(1)−Cterm 0.252 C(19)−C(20) 1.415(1)

ΔMn(2)−Cterm 0.223 C(20)−C(21) 1.405(1)

Mn…Mn 3.557(1) C(21)−C(26) 1.452(1)

Mn(1)−O(1) 2.037(2) C(26)−C(25) 1.426(1)

Mn(2)−O(1) 2.053(1) C(25)−C(1) 1.445(1)

131

Figure 66. Diagram of the non-‐hydrogen atoms of (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) with the numbering scheme used in the text. Thermal ellipsoids are shown at the 50% probability level.

[Mn(BHT)(THF)]2(µ-BHT)(µ-Cl). Crystals of (BHT)2(µ-BHT)Mn2(µ-Cl) were

harvested as pale yellow blocks from a room temperature solution of pentane. An

ORTEP of the unit cell is shown in Figure 67, which gives the numbering scheme that is

referred to in the text. Selected bond lengths and angles are shown in Table 6.

There are two types of BHT present in the molecule, as a bridging ligand between

the two Mn centers and as a terminal ligand on both Mn centers. The geometry around

each manganese is a slightly distorted tetrahedral with a near planar Mn2O2 core despite

having no crystallographically imposed symmetry. The structure is unique among

structurally characterized aryloxides of MnII, as this is the first compound to contain both

a bridging halide and aryloxide in addition to terminal aryloxides. This fact is surprising

given that attempts to make the compound with a 2:1 ratio of aryloxide ligand to Mn have

produced the same compound, suggesting an unusual stability of this particular complex.

132

The terminal Mn−O bonds have an average length of 1.902(4) Å, which falls in

the typical range for terminal MnII aryloxides (1.86-1.95 Å).186,187 The Mn−O−C angles

for the terminal aryloxide ligands average 162.6° (160.50 and 164.70), which is much

closer to linear than should be expected around an oxygen atom with sp3 hybridization.

This suggests a large amount of ionic character in this interaction, similar to what is

proposed by Bartlett et al in their homoleptic compounds from the early 1990s.186 More

recent compounds prepared by Deacon et al show a much smaller Mn−O−C angle for

terminal aryloxide ligands, but this is likely adopted to help alleviate steric strain of the

bulky aryloxide ligands that are crowded around a monomeric MnII center with a

tetrahedral geometry from coordinated DME.187

The bridging BHT group has an average Mn−O bond length of 2.060(5) Å, which

is very similar to the distance in (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT) for the same bridging

aryloxide group (2.04(1) Å). The Mn−Cl distances of 2.449(6) and 2.442(6) Å for the

bridging halide are also very close to those present for the chlorides in {(Ind3Me-

2,4,7)MnCl(thf)}2. The Mn---Mn distance of 3.282(3) Å is shorter than what is reported

for other dimeric Mn phenoxide compounds, but is still well outside the range typically

considered for metal−metal bonding.

Table 7. Selected bond distances for (BHT)2(µ-BHT)Mn2(µ-Cl).


Terminal Bridging

Mn(1)–O(1) 2.060(5) Mn(1)–Cl(1) 2.259(1)

Mn(1)–O(2) 2.353(1) Mn(2)–C(1) 2.282(2)

Mn(2)−O(1) 2.413(1) Mn(1)−O(2)−C(16) < 164.8°

Mn(2)−O(3) 2.576(2) Mn(2)−O(3)−C(31) < 160.5°

133

Figure 67. Diagram of the non-‐hydrogen atoms of (BHT)2(µ-BHT)Mn2(µ-Cl) with the numbering scheme used in the text. Thermal ellipsoids are shown at the 50% probability level.

Conclusions

Interest in aryloxide complexes of MnII came about from the isolation of (IndMe-

2)2(µ-IndMe-2)Mn2(µ-BHT) as an unexpected side product from the preparation of the

bis(indenyl)manganese compound. BHT was present as an inhibitor in the anhydrous

THF used for the reaction, and was deprotonated and then scavenged by the oxophilic

manganese center. The oxophilicity of MnII has been evidenced throughout this

dissertation, ranging from the inability to remove THF from the parent

bis(indenyl)manganese to the oxygen reactivity witnessed with mono(indenyl)manganese

halides. Additional evidence of its oxophilicity is provided by the multiple attempts to

remake the previously isolated (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT), only to instead obtain

(BHT)2(µ-BHT)Mn2(µ-Cl) and other compounds that lacked the presence of the indenyl

134

ligand. This indicates a strong preference of the Mn to coordinate phenoxide ligands over

the indenyl ligands, given that indenyl ligand was present in a 3:1 abundance compared

to the phenoxide.

Manganese(II) aryloxides are relatively rare, with fewer than 20 having been

reported in the literature. The synthesis routes proposed in this work represent a

straightforward method towards making these compounds in relatively high yields (>

70%) without having to use toxic reagents such as aryl mercury compounds during

synthesis. If monomeric complexes are desired, routes using slightly a bulkier

coordinating solvent such as DME could be attempted, and these methods are currently

under further investigation.

135

CHAPTER VI

PROJECT SUMMARY AND FUTURE RESEARCH

Summary

The indenyl ligand, while similar to the cyclopentadienyl ring, has greater

flexibility in its interactions with metal centers, which is reflected by the greater variety

of chemical bonding modes in the ligands for organometallic indenyl compounds in

comparison to analogous ones featuring Cp. This contrast can be seen in the case of

methyl substituted bis(indenyl)manganese complexes relative to their manganocene

counterparts, especially when there is only substitution on the benzo position of the

indenyl ligand, as the lack of steric bulk around the Mn center results in oligomeric or

polymeric structures. Additionally, there is a measureable difference in physical

properties between the two families of complexes, as manganocenes have access to both

low and high spin states, and their magnetic properties can be tuned by the electronic

properties of the Cp substituents. For the bis(indenyl)manganese compounds, there has

been no evidence of an accessible low spin state, and all compounds have been shown to

be high spin at all temperatures.

Methylated mono(indenyl)manganese halides also demonstrate that even in cases

where the structures of the indenyl compounds are very similar to that of their Cp

analogs, there can be stark differences in the chemical behavior between the species. The

mono(indenyl)manganese halides coordinate oxygen at low temperature and very low

concentrations, something that is not observed in the Cp compounds. Current analysis of

136

this interaction has lead to the conclusion that a MnIII superoxide is formed, but the full

excitation profile for the resonance Raman spectra, coupled with EPR simulations for the

proposed superoxide, will be needed to fully confirm this assignment.

A consistent trend seen with both the bis(indenyl)manganese complexes and the

mono(indenyl)manganese halides is the relatively high oxophilicity of the MnII center.

This is shown in the bis(indenyl) compounds by the inability to isolate THF-free

bis(indenyl)manganese, as once THF is coordinated to the metal center, it is difficult to

remove unless there is sufficient steric bulk on the indenyl ligand. The oxophilicity is

further displayed by the mono(indenyl) halide compounds, which will react with trace

quantities (< 5 ppm) of molecular oxygen. These observations, coupled with the isolation

of (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT), prompted attempts to synthesize MnII aryloxide

complexes, a relatively rare type of compound for manganese. These compounds could

be prepared from straightforward salt-metathesis elimination reactions, which represent a

marked improvement on previous synthetic routes involving aryl mercury reagents.187

Future Work

There are still several avenues for continued research on manganese(II) indenyl

compounds. For the bis(indenyl) compounds, synthesis of a monomeric methylated

bis(indenyl) species has not been achieved. This compound would be of interest for its

magnetic properties (e.g. its potential for assuming a low-spin state) and its incorporation

into a charge-transfer (CT) salt. Currently, the oligomeric and polymeric

bis(indenyl)manganese complexes do not favorably lend themselves to making

magnetically ordered CT salts due to their lack of a classic sandwich structure that

137

enables π stacking, a physical trait that has been linked to magnetic ordering. A

monomeric, methyl-substituted bis(indenyl)manganese compound could make such a CT

salt possible. Previous studies on the trimethylsilyl-substituted compounds indicated no

magnetic ordering in the associated CT salts, but methyl groups may be better suited for

this purpose.

For the methyl-substituted mono(indenyl)manganese halides, further analysis of

the resonance Raman and EPR data is needed to confirm the assignment of the oxo-

species as a MnIII superoxide compound. EPR can also be used in an attempt to quantify

the reactivity, and determine just how much oxygen is being coordinated. This can be

done using internal standards, but may be complicated if the EPR active species is

actually the bis(indenyl) complex formed from Schlenk-type rearrangement. This is

another reason why simulations to help confirm EPR assignments should be pursued.

Further investigation on the structural and electronic requirements for enabling

oxygen reactivity should also be examined. Thus far, it is observed for only [Ind3Me-

2,4,7MnCl(thf)]2, [IndMe-2MnCl(thf)]2, [IndMnCl(thf)]2, and [IndMe-2MnI(thf)]2, and forms

the most stable oxo-species with the chlorides, specifically [IndMe-2MnCl(thf)]2.

Preliminary results for [Ind3Me-1,2,3MnCl(thf)]2 suggest this compound does not react with

oxygen at the ppm levels, indicating that sufficient steric bulk on the front side of the

indenyl ligand may block oxygen access to the Mn center. This is counterintuitive when

electronics are considered, as the stronger donating trimethylindenyl ligand should be

expected to help promote superoxide formation relative to the methylindenyl ligand.

However, since this is not observed, it is likely that the steric bulk of the ligand has a

greater impact on reactivity than the electron donating effects of the ligand.

138

The MnII aryloxide chemistry can still benefit from optimizztion of the syntheses

and the development of both homoleptic and monomeric species. Use of bulkier

coordinating solvents may help to form monomeric species, as is found for some DME

solvates.187 Additional synthetic attempts using a larger excess of the phenoxide salts

may help to form homoleptic species, instead of the chloride-containing species currently

known. SQUID magnetometry may prove informative, as there is precedent for MnII

aryloxide compounds with ferromagnetic behavior.191 Further tests investigating their

potential to serve as hydrogenation or carbonylation catalysts can also be considered, as

metal alkoxides and aryloxides are presumed to be key components in the mechanisms of

both of these processes.

139

Appendix A

CRYSTAL DATA AND ATOMIC FRACTIONAL COORDINATES FOR X-RAY STRUCTURAL DETERMINTIONS

140

Table 8. Crystal data and structure refinement for [K(dioxane)1.5][(Mn(Ind2Me-4,7)3]. ________________________________________________________________________________

Empirical formula C234 H270 K6 Mn6 O18

Formula weight 3934.74

Temperature 100.0(1) K

Wavelength 0.71073 Å

Crystal system Hexagonal

Space group P63

Unit cell dimensions a = 19.125(5) Å α = 90°

b = 19.125(5) Å β = 90°

c = 32.076(8) Å γ = 120°

Volume 10160(4) Å3

Z 2

Density (calculated) 1.286 Mg/m3

Absorption coefficient 0.549 mm-1

F(000) 4164

Crystal color, morphology yellow, hexagonal plate

Crystal size 0.28 x 0.16 x 0.06 mm3

Theta range for data collection 1.77 to 31.51°

Index ranges -28 ≤ h ≤ 28, -28 ≤ k ≤ 28, -47 ≤ l ≤ 47

Reflections collected 132350

Independent reflections 22576 [R(int) = 0.1435]

Observed reflections 13455

Completeness to theta = 31.51° 100.0%

Absorption correction Multi-scan

Max. and min. transmission 0.9678 and 0.8616

Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 22576 / 14 / 822

Goodness-of-fit on F2 1.012

Final R indices [I>2sigma(I)] R1 = 0.0758, wR2 = 0.1770

R indices (all data) R1 = 0.1425, wR2 = 0.2191

Absolute structure parameter 0.21(2)

Largest diff. peak and hole 4.709 and -0.541 e.Å-3

141

Table 9. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103 ) for [K(dioxane)1.5][(Mn(Ind2Me-4,7)3]. Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

________________________________________________________________________________ x y z Ueq

________________________________________________________________________________

Mn1 6667 3333 6577(1) 20(1)

C1 5713(3) 3686(3) 6367(2) 21(1)

C2 5682(3) 3676(3) 6813(2) 25(1)

C3 5142(3) 2890(3) 6954(2) 22(1)

C4 4292(3) 1544(3) 6558(1) 18(1)

C5 4128(3) 1228(3) 6161(1) 21(1)

C6 4462(3) 1718(3) 5801(1) 20(1)

C7 4971(3) 2538(3) 5830(1) 18(1)

C8 5163(3) 2885(3) 6231(1) 19(1)

C9 4816(2) 2387(3) 6596(1) 18(1)

C10 3957(3) 1029(3) 6940(2) 28(1)

C11 5342(3) 3078(3) 5458(2) 26(1)

Mn2 0 0 6016(1) 21(1)

C12 1251(3) 1044(3) 6234(2) 23(1)

C13 1251(3) 1097(3) 5788(2) 22(1)

C14 1518(3) 595(3) 5621(2) 23(1)

C15 1974(3) -337(3) 5960(2) 22(1)

C16 2099(3) -573(3) 6339(2) 26(1)

C17 1973(3) -269(3) 6719(2) 25(1)

C18 1695(3) 268(3) 6727(2) 21(1)

C19 1541(3) 522(3) 6335(2) 18(1)

C20 1704(3) 228(3) 5954(1) 19(1)

C21 2121(3) -651(3) 5562(2) 34(1)

C22 1554(3) 594(3) 7124(2) 32(1)

Mn3 3333 6667 3474(1) 21(1)

C23 2969(3) 5357(3) 3676(2) 24(1)

C24 2999(3) 5340(3) 3227(2) 26(1)

C25 3786(3) 5595(3) 3100(2) 22(1)

C26 5121(3) 6086(3) 3509(2) 20(1)

142

C27 5424(3) 6243(3) 3908(2) 22(1)

C28 4916(3) 6080(3) 4263(2) 21(1)

C29 4091(3) 5752(3) 4226(1) 20(1)

C30 3766(3) 5604(3) 3818(1) 18(1)

C31 4269(3) 5756(2) 3459(1) 18(1)

C32 5637(3) 6262(3) 3132(2) 26(1)

C33 3549(3) 5589(3) 4596(2) 27(1)

Mn4 6667 3333 4079(1) 18(1)

C34 5655(3) 3568(3) 3867(1) 20(1)

C35 5579(3) 3523(3) 4306(2) 23(1)

C36 6064(3) 4295(3) 4479(1) 18(1)

C37 6984(3) 5690(3) 4141(2) 22(1)

C38 7244(3) 6056(3) 3752(2) 27(1)

C39 6979(3) 5617(3) 3381(2) 26(1)

C40 6449(3) 4797(3) 3371(2) 22(1)

C41 6185(3) 4413(3) 3763(2) 18(1)

C42 6440(3) 4844(3) 4143(2) 19(1)

C43 7243(3) 6160(3) 4544(2) 31(1)

C44 6141(4) 4318(4) 2974(2) 32(1)

Mn5 3333 6667 5998(1) 19(1)

C45 3065(3) 5394(3) 6195(2) 22(1)

C46 3063(3) 5361(3) 5749(2) 23(1)

C47 2279(3) 5123(3) 5607(2) 24(1)

C48 958(3) 4777(3) 5990(2) 24(1)

C49 642(3) 4696(3) 6380(2) 29(1)

C50 1113(3) 4822(3) 6747(2) 24(1)

C51 1915(3) 5058(3) 6728(2) 20(1)

C52 2266(3) 5141(2) 6327(2) 15(1)

C53 1781(3) 4981(3) 5955(2) 20(1)

C54 459(3) 4638(3) 5605(2) 36(1)

C55 2433(3) 5228(3) 7110(2) 26(1)

Mn6 0 0 4033(1) 25(1)

C56 1306(3) 938(3) 3879(2) 33(1)

C57 1324(3) 874(4) 4320(2) 41(1)

C58 1507(3) 275(4) 4431(2) 38(1)

C59 1815(3) -655(3) 3983(2) 27(1)

143

C60 1911(3) -819(3) 3580(2) 26(1)

C61 1814(3) -408(3) 3242(2) 27(1)

C62 1622(3) 191(3) 3300(2) 24(1)

C63 1527(3) 379(3) 3712(2) 25(1)

C64 1634(3) -46(3) 4054(2) 27(1)

C65 1884(3) -1145(4) 4336(2) 40(1)

C66 1472(3) 614(3) 2946(2) 31(1)

K1 3079(1) 1980(1) 6056(1) 20(1)

K2 4673(1) 4443(1) 3978(1) 20(1)

O1 3554(2) 3303(2) 3536(1) 32(1)

C67 3489(4) 2606(3) 3339(2) 44(2)

C68 3378(4) 2647(4) 2877(2) 46(2)

O2 2691(2) 2702(2) 2783(1) 36(1)

C69 2753(4) 3393(3) 2988(2) 32(1)

C70 2856(3) 3362(3) 3447(2) 27(1)

O3 3583(2) 3647(2) 4596(1) 32(1)

C71 3964(4) 4010(3) 4976(2) 39(1)

C72 3396(5) 3620(3) 5334(2) 49(2)

O4 3148(2) 2794(2) 5355(1) 39(1)

C73 2744(3) 2416(3) 4976(2) 38(1)

C74 3292(3) 2800(3) 4601(2) 36(1)

O5 3200(2) 3221(2) 6448(1) 33(1)

C75 2548(14) 3280(30) 6645(8) 50(5)

C76 2636(13) 3329(17) 7105(8) 61(6)

O6 3396(13) 4008(18) 7238(7) 45(3)

C77 4051(12) 3960(20) 7038(8) 37(3)

C78 3942(10) 3900(20) 6579(8) 29(3)

C75' 2526(12) 3340(20) 6529(7) 50(5)

C76' 2402(11) 3303(14) 6988(8) 61(6)

O6' 3132(12) 3923(15) 7185(6) 45(3)

C77' 3837(12) 3865(19) 7090(6) 37(3)

C78' 3923(9) 3850(17) 6631(7) 29(3)

________________________________________________________________________________

144

Table 10. Crystal data and structure refinement for (Ind3Me-2,4,7)2Mn. ________________________________________________________________________________

Empirical formula C24 H26 Mn




Crystal system Tetragonal

Space group I41/a


b = 27.094(5) Å β = 90°

c = 10.212(2) Å γ = 90°

Volume 7496(3) Å3

Z 16



F(000) 3120

Crystal color, morphology orange, needle



Index ranges -35 ≤ h ≤ 35, -35 ≤ k ≤ 35, -13 ≤ l ≤ 13













145

Table 11. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103 ) for (Ind3Me-2,4,7)2Mn. Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

________________________________________________________________________________ x y z Ueq

________________________________________________________________________________

Mn1 1358(1) 4394(1) 4147(1) 20(1)

C1 714(1) 4433(1) 5927(3) 24(1)

C2 632(1) 4786(1) 4941(3) 25(1)

C3 535(1) 4535(1) 3744(3) 26(1)

C4 415(1) 3598(1) 3239(3) 26(1)

C5 428(1) 3141(1) 3826(3) 28(1)

C6 555(1) 3080(1) 5162(3) 26(1)

C7 660(1) 3474(1) 5955(3) 22(1)

C8 637(1) 3952(1) 5389(3) 21(1)

C9 529(1) 4015(1) 4016(3) 23(1)

C10 626(1) 5336(1) 5159(4) 31(1)

C11 262(1) 3662(1) 1838(3) 38(1)

C12 781(1) 3414(1) 7382(3) 27(1)

C13 1906(1) 3886(1) 5195(3) 19(1)

C14 2171(1) 4266(1) 5860(3) 19(1)

C15 2632(1) 4330(1) 5222(3) 20(1)

C16 3032(1) 3892(1) 3210(3) 22(1)

C17 2952(1) 3506(1) 2351(3) 24(1)

C18 2530(1) 3202(1) 2419(3) 25(1)

C19 2160(1) 3290(1) 3326(3) 22(1)

C20 2222(1) 3697(1) 4165(3) 20(1)

C21 2659(1) 3985(1) 4141(3) 19(1)

C22 1994(1) 4542(1) 7038(3) 25(1)

C23 3504(1) 4180(1) 3213(3) 29(1)

C24 1718(1) 2961(1) 3448(3) 28(1) ________________________________________________________________________________

146

Table 12. Crystal data and structure refinement for [Ind3Me-2,4,7MnCl(thf)]2. ________________________________________________________________________________

Empirical formula C32 H42 Cl2 Mn2 O2




Crystal system Triclinic

Space group P-1

Unit cell dimensions a = 9.5845(5) Å α = 85.269(1)°

b = 9.6973(5) Å β = 88.141(1)°

c = 17.1564(10) Å γ = 83.660(1)°

Volume 1578.99(15) Å3

Z 2



F(000) 668

Crystal color, morphology yellow, block



Index ranges -15 ≤ h ≤ 15, -15 ≤ k ≤ 15, -28 ≤ l ≤ 28













147

Table 13. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103 ) for [Ind3Me-2,4,7MnCl(thf)]2. Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

________________________________________________________________________________ x y z Ueq

________________________________________________________________________________

Mn1 4312(1) 8590(1) 433(1) 41(1)

Cl1 6286(1) 8858(1) -466(1) 51(1)

C1 4865(2) 8096(2) 1743(1) 44(1)

C2 5567(2) 6986(2) 1355(1) 46(1)

C3 4577(2) 6165(2) 1109(1) 46(1)

C4 1880(2) 6249(2) 1355(2) 56(1)

C5 784(2) 7034(3) 1692(2) 67(1)

C6 939(2) 8267(3) 2031(2) 60(1)

C7 2221(2) 8748(2) 2074(1) 50(1)

C8 3396(2) 7936(2) 1773(1) 39(1)

C9 3234(2) 6707(2) 1386(1) 42(1)

C10 7135(2) 6713(3) 1245(1) 64(1)

C11 1712(3) 4939(3) 978(2) 87(1)

C12 2391(3) 10079(3) 2437(2) 69(1)

O1 2788(1) 8334(2) -375(1) 52(1)

C13 2945(3) 7639(3) -1078(2) 68(1)

C14 1510(3) 7790(4) -1423(2) 80(1)

C15 518(3) 8173(3) -779(2) 71(1)

C16 1348(2) 8953(3) -289(1) 58(1)

Mn2 6246(1) 786(1) 4464(1) 33(1)

Cl2 6324(1) -1315(1) 5345(1) 41(1)

C17 8505(2) 524(2) 3600(1) 35(1)

C18 7461(2) -280(1) 3379(1) 35(1)

C19 6279(2) 623(2) 3129(1) 33(1)

C20 5806(2) 3320(2) 2969(1) 35(1)

C21 6464(2) 4498(2) 3041(1) 44(1)

C22 7847(2) 4426(2) 3298(1) 47(1)

C23 8639(2) 3194(2) 3505(1) 41(1)

C24 8002(2) 1953(1) 3447(1) 32(1)

148

C25 6600(2) 2025(1) 3164(1) 30(1)

C26 7599(2) -1838(2) 3395(1) 47(1)

C27 4343(2) 3375(2) 2680(1) 45(1)

C28 10143(2) 3120(2) 3742(2) 63(1)

O2 6816(1) 2172(1) 5247(1) 44(1)

C29 6138(11) 3608(8) 5181(5) 48(2)

C30 7125(6) 4453(4) 5559(3) 68(1)

C31 7861(6) 3389(4) 6153(3) 68(1)

C32 8110(20) 2087(16) 5670(20) 71(1)

C29' 6154(15) 3555(12) 5370(8) 48(2)

C30' 7055(8) 4077(7) 5952(4) 68(1)

C31' 8524(8) 3419(6) 5779(4) 68(1)

C32' 8170(30) 1930(20) 5620(30) 71(1) ________________________________________________________________________________

149

Table 14. Crystal data and structure refinement for [IndMe-2MnI(thf)]2. ________________________________________________________________________________

Empirical formula C28 H34 I2 Mn2 O2





Space group P-1


b = 9.3747(6) Å β = 86.954(1)°

c = 9.6781(6) Å γ = 80.887(1)°

Volume 715.80(8) Å3

Z 1



F(000) 374

Crystal color, morphology yellow-green, block



Index ranges -13 ≤ h ≤ 13, -15 ≤ k ≤ 15, -16 ≤ l ≤ 16













150

Table 15. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103 ) for [IndMe-2MnI(thf)]2. Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

________________________________________________________________________________ x y z Ueq

________________________________________________________________________________

Mn1 3673(1) 6428(1) 926(1) 17(1)

I1 5205(1) 6522(1) -1732(1) 21(1)

C1 788(2) 6333(2) 1215(2) 19(1)

C2 873(2) 7515(2) 213(1) 18(1)

C3 1389(2) 8660(2) 862(2) 18(1)

C4 1886(2) 8980(2) 3447(2) 25(1)

C5 1913(3) 8268(2) 4746(2) 31(1)

C6 1636(2) 6820(2) 4953(2) 30(1)

C7 1277(2) 6074(2) 3872(2) 25(1)

C8 1171(2) 6782(2) 2530(2) 18(1)

C9 1520(2) 8247(2) 2307(2) 18(1)

C10 410(2) 7558(2) -1274(2) 23(1)

O1 5478(2) 7305(1) 1957(1) 23(1)

C11 5842(3) 8756(2) 1512(2) 33(1)

C12 7047(3) 9089(2) 2520(2) 34(1)

C13 6676(3) 8163(2) 3837(2) 34(1)

C14 6237(3) 6807(2) 3271(2) 31(1) ________________________________________________________________________________

151

Table 16. Crystal data and structure refinement for (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT). ________________________________________________________________________________

Empirical formula C45 H50 Mn2 O




Crystal system Monoclinic

Space group P21/c


b = 10.3790(10) Å β = 110.487(2)°

c = 18.8577(17) Å γ = 90°

Volume 3639.0(6) Å3

Z 4



F(000) 1512

Crystal color, morphology yellow, block



Index ranges -33 ≤ h ≤ 34, -17 ≤ k ≤ 17, -32 ≤ l ≤ 32













152

Table 17. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103 ) for (IndMe-2)2(µ-IndMe-2)Mn2(µ-BHT). Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

________________________________________________________________________________ x y z Ueq

________________________________________________________________________________

Mn1 8517(1) 862(1) 2495(1) 18(1)

Mn2 6816(1) -521(1) 2276(1) 25(1)

O1 7506(1) 335(1) 1823(1) 16(1)

C1 9077(1) 2845(1) 2372(1) 24(1)

C2 9195(1) 1926(2) 1869(1) 25(1)

C3 9656(1) 956(2) 2303(1) 25(1)

C4 10333(1) 715(2) 3748(1) 27(1)

C5 10428(1) 1282(2) 4435(1) 31(1)

C6 10075(1) 2436(2) 4483(1) 31(1)

C7 9621(1) 3036(2) 3844(1) 26(1)

C8 9515(1) 2487(1) 3129(1) 22(1)

C9 9877(1) 1311(1) 3082(1) 22(1)

C10 5583(3) 203(5) 1754(3) 31(1)

C11 5651(3) -921(5) 1365(2) 32(1)

C12 5775(5) -1964(5) 1872(3) 30(1)

C13 5829(7) -2165(10) 3290(4) 30(1)

C14 5714(10) -1432(9) 3852(6) 40(2)

C15 5582(7) -117(9) 3755(5) 38(2)

C16 5530(7) 508(9) 3106(5) 33(1)

C17 5591(9) -216(7) 2496(6) 23(1)

C18 5747(1) -1578(1) 2593(1) 23(1)

C29 5526(3) -1005(7) 527(2) 61(2)

C10' 5633(4) -212(6) 1647(4) 31(1)

C11' 5726(3) -1444(6) 1404(3) 32(1)

C12' 5842(6) -2306(6) 1992(4) 30(1)

C13' 5734(8) -2008(13) 3297(5) 30(1)

C14' 5685(12) -1088(12) 3807(8) 40(2)

C15' 5566(9) 202(11) 3609(7) 38(2)

C16' 5547(10) 613(11) 2924(7) 33(1)

153

C17' 5661(12) -244(9) 2416(7) 23(1)

C18' 5747(1) -1578(1) 2593(1) 23(1)

C29' 5637(4) -1803(8) 604(3) 61(2)

C19 8572(1) 100(1) 3636(1) 20(1)

C20 7920(1) 496(1) 3715(1) 20(1)

C21 7431(1) -536(1) 3550(1) 20(1)

C22 7607(1) -2963(1) 3291(1) 24(1)

C23 8100(1) -3841(2) 3215(1) 29(1)

C24 8784(1) -3443(2) 3244(1) 29(1)

C25 8991(1) -2169(2) 3363(1) 25(1)

C26 8507(1) -1263(1) 3466(1) 19(1)

C27 7805(1) -1662(1) 3418(1) 20(1)

C28 8907(1) 1994(2) 1017(1) 34(1)

C30 7796(1) 1787(2) 4000(1) 28(1)

C31 7222(1) 514(1) 1047(1) 16(1)

C32 7298(1) -490(1) 567(1) 16(1)

C33 6986(1) -313(1) -211(1) 19(1)

C34 6606(1) 791(1) -532(1) 19(1)

C35 6555(1) 1755(1) -49(1) 20(1)

C36 6851(1) 1661(1) 741(1) 18(1)

C37 7726(1) -1739(1) 866(1) 19(1)

C38 7669(1) -2691(1) 229(1) 26(1)

C39 7468(1) -2455(2) 1429(1) 38(1)

C40 8526(1) -1429(2) 1248(1) 35(1)

C41 6263(1) 923(1) -1377(1) 25(1)

C42 6766(1) 2887(1) 1171(1) 23(1)

C43 7011(1) 2798(2) 2038(1) 29(1)

C44 7200(1) 3977(2) 984(1) 34(1)

C45 5972(1) 3309(2) 904(1) 33(1)

________________________________________________________________________________

154

Table 18. Crystal data and structure refinement for (BHT)2(µ-BHT)Mn2(µ-Cl). ________________________________________________________________________________

Empirical formula C58 H97 Cl Mn2 O5





Space group P-1


b = 17.593(3) Å β = 91.821(4)°

c = 22.018(4) Å γ = 91.897(4)°

Volume 5763(2) Å3

Z 4



F(000) 2208

Crystal color, morphology colorless, block



Index ranges -26 ≤ h ≤ 26, -29 ≤ k ≤ 26, 0 ≤ l ≤ 36













155

Table 19. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (Å2x 103 ) for (BHT)2(µ-BHT)Mn2(µ-Cl). Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

________________________________________________________________________________ x y z Ueq

________________________________________________________________________________

Mn1 1394(1) 9801(1) 2492(1) 19(1)

Mn2 3424(1) 10038(1) 2580(1) 18(1)

Cl1 2413(1) 10294(1) 3428(1) 26(1)

O1 2400(1) 9710(1) 1926(1) 18(1)

O2 383(1) 10263(1) 2372(1) 23(1)

O3 4361(1) 9364(1) 2357(1) 21(1)

C1 2540(1) 9525(1) 1273(1) 18(1)

C2 2568(1) 8682(1) 832(1) 18(1)

C3 2813(1) 8514(1) 194(1) 20(1)

C4 3024(1) 9130(1) -23(1) 22(1)

C5 2947(1) 9940(1) 407(1) 22(1)

C6 2689(1) 10164(1) 1048(1) 18(1)

C7 2269(1) 7964(1) 1012(1) 25(1)

C8 2697(2) 7957(1) 1645(1) 31(1)

C9 1335(2) 8024(1) 1088(1) 33(1)

C10 2410(2) 7117(1) 465(1) 44(1)

C11 3331(2) 8920(1) -703(1) 33(1)

C12 2628(1) 11104(1) 1452(1) 21(1)

C13 2164(2) 11485(1) 1026(1) 29(1)

C14 3502(1) 11510(1) 1627(1) 27(1)

C15 2146(1) 11351(1) 2086(1) 26(1)

C16 -385(1) 10526(1) 2416(1) 19(1)

C17 -662(1) 11084(1) 3029(1) 21(1)

C18 -1488(1) 11292(1) 3057(1) 23(1)

C19 -2047(1) 10991(1) 2518(1) 24(1)

C20 -1748(1) 10485(1) 1919(1) 24(1)

C21 -933(1) 10242(1) 1846(1) 21(1)

C22 -86(1) 11461(1) 3650(1) 24(1)

C23 662(2) 11922(1) 3519(1) 32(1)

156

C24 199(1) 10790(1) 3881(1) 27(1)

C25 -513(2) 12091(2) 4236(1) 33(1)

C26 -2947(1) 11186(1) 2578(1) 31(1)

C27 -673(1) 9638(1) 1170(1) 26(1)

C28 -577(2) 8791(1) 1203(1) 33(1)

C29 -1327(2) 9512(2) 616(1) 40(1)

C30 127(2) 9935(2) 960(1) 31(1)

C31 5148(1) 9218(1) 2450(1) 17(1)

C32 5706(1) 9099(1) 1938(1) 18(1)

C33 6535(1) 8996(1) 2061(1) 20(1)

C34 6839(1) 8999(1) 2658(1) 21(1)

C35 6280(1) 9068(1) 3134(1) 19(1)

C36 5436(1) 9159(1) 3047(1) 18(1)

C37 5408(1) 9051(1) 1253(1) 19(1)

C38 5043(1) 9863(1) 1294(1) 27(1)

C39 4755(1) 8336(1) 940(1) 24(1)

C40 6113(1) 8881(1) 773(1) 24(1)

C41 7753(1) 8933(1) 2775(1) 26(1)

C42 4846(1) 9197(1) 3592(1) 23(1)

C43 5266(1) 8968(2) 4127(1) 30(1)

C44 4556(1) 10077(1) 3943(1) 27(1)

C45 4102(1) 8575(1) 3310(1) 28(1)

O7 926(1) 8794(1) 2724(1) 26(1)

C91 50(1) 8622(1) 2742(1) 30(1)

C92 -22(2) 8433(2) 3349(1) 35(1)

C93 738(2) 7944(1) 3328(1) 32(1)

C94 1378(2) 8336(2) 3043(2) 43(1)

O8 4041(1) 11247(1) 3032(1) 25(1)

C95 3698(2) 11993(2) 3496(1) 39(1)

C96 4335(7) 12664(7) 3625(7) 55(1)

C97 5051(8) 12299(7) 3271(8) 60(2)

C98 4931(1) 11398(2) 3014(1) 32(1)

C95' 3698(2) 11993(2) 3496(1) 39(1)

C96' 4407(2) 12468(3) 3935(2) 55(1)

C97' 5132(3) 12246(3) 3537(3) 60(2)

C98' 4931(1) 11398(2) 3014(1) 32(1)

157

Mn3 6559(1) 5166(1) 2486(1) 19(1)

Mn4 8525(1) 4756(1) 2428(1) 18(1)

Cl2 7465(1) 4581(1) 1562(1) 24(1)

O4 7601(1) 5239(1) 3072(1) 17(1)

O5 5518(1) 4778(1) 2658(1) 24(1)

O6 9594(1) 5300(1) 2628(1) 22(1)

C46 7629(1) 5517(1) 3750(1) 16(1)

C47 7571(1) 4936(1) 4047(1) 17(1)

C48 7597(1) 5243(1) 4735(1) 19(1)

C49 7656(1) 6079(1) 5130(1) 21(1)

C50 7708(1) 6628(1) 4825(1) 21(1)

C51 7708(1) 6376(1) 4139(1) 17(1)

C52 7553(1) 3988(1) 3666(1) 18(1)

C53 8447(1) 3740(1) 3528(1) 25(1)

C54 7021(1) 3653(1) 3013(1) 22(1)

C55 7207(1) 3537(1) 4082(1) 24(1)

C56 7667(2) 6369(1) 5872(1) 31(1)

C57 7743(1) 7072(1) 3874(1) 19(1)

C58 8252(2) 7836(1) 4354(1) 30(1)

C59 8131(1) 6851(1) 3204(1) 22(1)

C60 6860(1) 7330(2) 3824(1) 32(1)

C61 4719(1) 4541(1) 2590(1) 18(1)

C62 4354(1) 3993(1) 1968(1) 19(1)

C63 3512(1) 3792(1) 1927(1) 21(1)

C64 3010(1) 4084(1) 2458(1) 21(1)

C65 3384(1) 4593(1) 3063(1) 19(1)

C66 4223(1) 4827(1) 3152(1) 18(1)

C67 4862(1) 3625(1) 1354(1) 24(1)

C68 5567(2) 3135(1) 1485(1) 31(1)

C69 5194(1) 4299(2) 1138(1) 29(1)

C70 4341(2) 3011(2) 756(1) 33(1)

C71 2095(1) 3867(1) 2381(1) 28(1)

C72 4589(1) 5390(1) 3841(1) 22(1)

C73 3954(1) 5580(1) 4375(1) 28(1)

C74 5296(2) 4977(2) 4056(1) 38(1)

C75 4900(2) 6216(2) 3842(1) 36(1)

158

C76 10359(1) 5579(1) 2596(1) 18(1)

C77 10926(1) 5791(1) 3152(1) 19(1)

C78 11736(1) 6037(1) 3095(1) 23(1)

C79 12011(1) 6085(1) 2520(1) 25(1)

C80 11439(1) 5918(1) 1996(1) 23(1)

C81 10612(1) 5676(1) 2017(1) 20(1)

C82 10669(1) 5741(1) 3800(1) 23(1)

C83 10459(2) 4843(1) 3695(1) 30(1)

C84 9925(1) 6265(2) 4067(1) 30(1)

C85 11361(1) 6063(2) 4347(1) 31(1)

C86 12909(1) 6299(2) 2472(1) 37(1)

C87 10007(1) 5530(1) 1426(1) 22(1)

C88 10400(2) 5752(2) 888(1) 30(1)

C89 9709(1) 4616(1) 1092(1) 26(1)

C90 9272(1) 6092(1) 1648(1) 27(1)

O9 6172(1) 6176(1) 2245(1) 28(1)

C99 5340(2) 6482(2) 2336(1) 33(1)

C100 5189(2) 6836(2) 1822(2) 49(1)

C101 5938(2) 6687(2) 1432(2) 48(1)

C102 6595(2) 6554(2) 1856(1) 41(1)

O10 8887(1) 3488(1) 2001(1) 25(1)

C103 8393(2) 2772(2) 1554(1) 43(1)

C104 8948(5) 2080(4) 1272(4) 45(2)

C105 9817(4) 2517(4) 1401(4) 50(1)

C106 9729(2) 3244(2) 2052(1) 35(1)

C03' 8393(2) 2772(2) 1554(1) 43(1)

C04' 9012(7) 2230(6) 1142(6) 45(2)

C05' 9732(6) 2320(5) 1625(5) 50(1)

C06' 9729(2) 3244(2) 2052(1) 35(1)

C107 3467(2) 7881(2) 4951(2) 67(1)

C108 3104(2) 8699(2) 5313(2) 71(1)

C109 2389(2) 8875(2) 4956(1) 42(1)

C110 1990(2) 9685(2) 5329(2) 48(1)

C111 1260(2) 9832(2) 4969(1) 45(1)

C112 3690(5) 5340(6) 201(5) 50(1)

C113 3068(3) 5026(3) 551(2) 43(1)

159

C114 2627(3) 4203(3) 118(2) 43(1)

C115 2052(3) 3857(3) 467(2) 46(1)

C116 1634(9) 3032(7) 71(5) 90(3)

C12' 3469(9) 5154(11) 218(10) 50(1)

C13' 2745(5) 4678(6) 338(4) 43(1)

C14' 2459(5) 3903(5) -228(4) 43(1)

C15' 1675(5) 3493(5) -131(4) 46(1)

C16' 1734(18) 3153(14) 386(9) 90(3) ________________________________________________________________________________

160

Appendix B

SOLID STATE MAGNETIC DATA

161

Table 20. SQUID data for [(Ind3Me-2,4,7)MnCl(thf)]2.

Temp (K) χm µ eff 1/χm χmT 5.00 0.02599 1.02 38.48 0.13 10.00 0.03975 1.78 25.15 0.40 14.99 0.04473 2.32 22.36 0.67 19.99 0.04698 2.74 21.29 0.94 24.98 0.04833 3.11 20.69 1.21 30.00 0.04934 3.44 20.27 1.48 35.00 0.05010 3.75 19.96 1.75 40.00 0.05074 4.03 19.71 2.03 45.00 0.05123 4.29 19.52 2.31 50.02 0.05181 4.55 19.30 2.59 55.06 0.05207 4.79 19.20 2.87 60.08 0.05138 4.97 19.46 3.09 65.08 0.05119 5.16 19.54 3.33 70.10 0.05086 5.34 19.66 3.57 75.12 0.05044 5.51 19.82 3.79 80.13 0.04994 5.66 20.03 4.00 85.14 0.04936 5.80 20.26 4.20 90.15 0.04873 5.93 20.52 4.39 95.18 0.04805 6.05 20.81 4.57 100.21 0.04734 6.16 21.12 4.74 105.21 0.04661 6.26 21.46 4.90 110.20 0.04586 6.36 21.81 5.05 115.24 0.04510 6.45 22.17 5.20 120.24 0.04435 6.53 22.55 5.33 125.24 0.04359 6.61 22.94 5.46 130.27 0.04284 6.68 23.34 5.58 135.28 0.04209 6.75 23.76 5.69 140.30 0.04136 6.81 24.18 5.80 145.31 0.04065 6.87 24.60 5.91 150.33 0.03995 6.93 25.03 6.00 155.33 0.03926 6.99 25.47 6.10 160.35 0.03860 7.04 25.91 6.19 165.36 0.03796 7.09 26.34 6.28 170.37 0.03734 7.13 26.78 6.36 175.39 0.03674 7.18 27.22 6.44 180.40 0.03615 7.22 27.66 6.52 185.41 0.03558 7.26 28.11 6.60 190.41 0.03501 7.30 28.57 6.67 195.43 0.03445 7.34 29.03 6.73 200.43 0.03390 7.37 29.50 6.79 205.45 0.03339 7.41 29.95 6.86 210.46 0.03285 7.44 30.44 6.91 215.44 0.03235 7.47 30.91 6.97

162

Temp (K) χm µ eff 1/χm χmT

220.44

0.03186

7.50

31.39

7.02 225.45 0.03138 7.52 31.87 7.07 230.44 0.03091 7.55 32.36 7.12 235.45 0.03045 7.57 32.84 7.17 240.47 0.03001 7.60 33.33 7.22 245.46 0.02957 7.62 33.82 7.26 250.47 0.02915 7.64 34.30 7.30 255.46 0.02874 7.66 34.79 7.34 260.46 0.02834 7.68 35.29 7.38 265.47 0.02794 7.70 35.79 7.42 270.45 0.02756 7.72 36.29 7.45 275.46 0.02718 7.74 36.79 7.49 280.46 0.02682 7.76 37.29 7.52 285.47 0.02646 7.77 37.79 7.55 290.47 0.02612 7.79 38.29 7.59 295.47 0.02578 7.81 38.79 7.62 300.47 0.02545 7.82 39.30 7.65

163

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